Exfoliating method, transferring method of thin film device, and thin film device, thin film integrated circuit device, and liquid crystal display device produced by the same

ABSTRACT

A transferring method including providing a substrate, forming a transferred layer over the substrate, joining a transfer member to the transferred layer, and removing the transferred layer from the substrate. The transferring method further includes transferring the transferred layer to the transfer member and reusing the substrate for another transfer. The transferring method may also include providing a substrate, forming a separation layer over the substrate, forming a transferred layer over the separation layer, and partly cleaving the separation layer such that a part of the transferred layer is transferred to a transfer member in a given pattern. The transferring method may also include joining a transfer member to the transferred layer, removing the transferred layer from the substrate and transferring the transferred layer to the transfer member, these of which constitute a transfer process, the transfer process being repeatedly performed.

TECHNICAL FIELD

[0001] The present invention relates to a method for exfoliating adetached member, and in particular, a transferring method forexfoliating a transferred layer comprising a thin film such as afunctional thin film and for transferring it onto a transfer member suchas a transparent substrate. Also, the present invention relates to atransferring method of a thin film device, a thin film device, a thinfilm integrated circuit device, and a liquid crystal display deviceproduced using the same.

BACKGROUND ART

[0002] Production of liquid crystal displays using thin film transistors(TFTs), for example, includes a step for forming thin film transistorson a transparent substrate by a CVD process or the like.

[0003] The thin film transistors are classified into those usingamorphous silicon (a-Si) and those using polycrystalline silicon (p-Si),and those using polycrystalline silicon are classified into those formedby a high temperature process and those formed by a low temperatureprocess.

[0004] Since the formation of such thin film transistors on a substrateinvolves treatment at a relatively high temperature, a heat resistantmaterial, that is, a material having a high softening point and a highmelting point must be used as the transparent substrate. At present, inthe production of TFTs by high temperature processes, transparentsubstrates composed of quartz glass which are sufficiently resistive toa temperature of approximately 1,000° C. are used. When TFTs areproduced by low temperature processes, the maximum process temperatureis near 500° C., hence heat-resisting glass which is resistive to atemperature near 500° C. is used.

[0005] As described above, a substrate for use in forming thin filmdevices must satisfy the conditions for producing these thin filmdevices. The above-mentioned “substrate” is, however, not alwayspreferable in view of only the steps after fabrication of the substrateprovided with thin film devices is completed.

[0006] For example, in the production process with high temperaturetreatment, quartz glass or heat-resisting glass is used, however, theyare rare and very expensive materials, and a large transparent substratecan barely be produced from the material.

[0007] Further, quartz glass and heat-resisting glass are fragile,easily broken, and heavy. These are severe disadvantages when asubstrate provided with thin film devices such as TFTs is mounted intoelectronic units. There is a gap between restriction due to processconditions and preferred characteristics required for products, hence itis significantly difficult to satisfy both the restriction andcharacteristics.

[0008] The present invention has been achieved in view of such aproblem, and has an object to provide an exfoliating method, whichpermits easy exfoliation regardless of characteristics of the detachedmember and conditions for exfoliating, and transferring to varioustransfer members. Another object is to provide a novel technology whichis capable of independently selecting a substrate used in production ofthin film devices and a substrate used when the product is used (asubstrate having preferable properties for use of the product). Afurther object is to provide a novel technology not causingdeterioration of characteristics of thin film devices which aretransferred onto a substrate, by decreasing the optical energy radiatedto the separable layer causing ablation in the transferring process.

DISCLOSURE OF INVENTION

[0009] 1. First, a method for exfoliating a detached member or atransferred layer from a substrate for production is disclosed. Theinventions are as follows:

[0010] (1) An exfoliating method in accordance with the presentinvention is a method for exfoliating a detached member, which ispresent on a substrate with a separation layer therebetween, from thesubstrate, wherein the separation layer is irradiated with incidentlight so as to cause exfoliation in the separation layer and/or at theinterface, and to detach the detached member from the substrate.

[0011] (2) A method for exfoliating a detached member, which is presenton a transparent substrate with a separation layer therebetween, fromthe substrate, wherein the separation layer is irradiated with incidentlight from the side of the substrate so as to cause exfoliation in theseparation layer and/or at the interface, and to detach the detachedmember from the substrate.

[0012] (3) A method for exfoliating a transferred layer formed on asubstrate with a separation layer therebetween from the substrate andtransferring the transferred layer onto a transfer member, wherein afterthe transfer member is adhered to the opposite side of the transferredlayer to the substrate, the separation layer is irradiated with incidentlight so as to cause exfoliation in the separation layer and/or at theinterface, and to detach the transferred layer from the substrate totransfer onto the transfer member.

[0013] (4) A method for exfoliating a transferred layer formed on atransparent substrate with a separation layer therebetween from thesubstrate and transferring the transferred layer onto a transfer member,wherein after the transfer member is adhered to the opposite side of thetransferred layer to the substrate, the separation layer is irradiatedwith incident light from the side of the substrate so as to causeexfoliation in the separation layer and/or at the interface, and todetach the transferred layer from the substrate to transfer onto thetransfer member.

[0014] (5) An exfoliating method includes a step for forming aseparation layer on a transparent substrate, a step for forming atransferred layer on the separation layer directly or with a giveninterlayer therebetween, a step for adhering the transfer member to theopposite side of the transferred layer to the substrate, and a step forirradiating the separation layer with incident light from the side ofthe substrate so as to cause exfoliation in the separation layer and/orat the interface, and to detach the transferred layer from the substrateto transfer onto the transfer member.

[0015] In connection with these inventions, the following inventions aredisclosed.

[0016] After transferring the transferred layer onto the transfermember, a step for removing the separation layer adhering to the side ofthe substrate and/or transfer member may be provided.

[0017] A functional thin film or a thin film device may be used as thetransferred layer. Particularly, a thin film transistor is preferablyused as the transferred layer. Preferably, the transfer member is atransparent substrate.

[0018] When the maximum temperature in the formation of the transferredlayer is Tmax, it is preferred that the transfer member be composed of amaterial having a glass transition point (Tg) or softening point whichis lower than Tmax. Particularly, it is preferred that the transfermember be composed of a material having a glass transition point (Tg) orsoftening point which is lower than 800° C.

[0019] It is preferable that the transfer member be composed of asynthetic resin or glass.

[0020] It is preferable that the substrate has thermal resistance. Inparticular, when the maximum temperature in the formation of thetransferred layer is Tmax, it is preferred that the substrate becomposed of a material having a distortion point which is lower thanTmax.

[0021] In the above-mentioned exfoliating methods, the exfoliation ofthe separation layer is caused by an elimination of or a decrease in theadhering force between atoms or molecules in the constituent substancesin the separation layer.

[0022] It is preferable that the incident light be laser light.Preferably, the laser light has a wavelength of 100 nm to 350 nm.Alternatively, the laser light has a wavelength of 350 nm to 1,200 nm.

[0023] It is preferable that the separation layer is composed ofamorphous silicon. Preferably, the amorphous silicon contains 2 atomicpercent or more of hydrogen (H).

[0024] The separation layer may be composed of a ceramic. Alternatively,the separation layer may be composed of a metal. Alternatively, theseparation layer may be composed of an organic polymer. In this case, itis preferable that the organic polymer has at least one adhere selectedfrom the group consisting of —CH₂—, —CO—, —CONH—, —NH—, —COO—, —N═N—,and —CH═N—. Further, it is preferable that the organic polymer has anaromatic hydrocarbon group in the chemical formula.

[0025] 2. Next, inventions in which the above-mentioned separation layerincludes a plurality of composites are disclosed. These inventions areas follows.

[0026] First, the separation layer in the inventions disclosed inparagraph 1 includes a composite with a plurality of layers. Further,the separation layer includes at least two layers having differentcompositions or characteristics.

[0027] It is preferable that the separation layer includes an opticalabsorption layer for absorbing the incident light and another layerhaving a different composition or property from the optical absorptionlayer. Preferably, the separation layer includes the optical absorptionlayer for absorbing the incident light and a shading layer for shadingthe incident light. Preferably, the shading layer lies at the oppositeside of the optical absorption layer to the incident light. Preferably,the shading layer is a reflection layer for reflecting the incidentlight. Preferably, the reflection layer is composed of a metallic thinfilm.

[0028] 3. A method for transferring a thin film device, which is used asa detached member or a transferred member, will now be disclosed.

[0029] A method for transferring a thin film device on a substrate ontoa transferred member includes: a step for forming a separation layer onthe substrate; a step for forming a transferred layer including the thinfilm device onto the separation layer; a step for adhering thetransferred layer including the thin film device to the transfer memberwith an adhesive layer, a step for irradiating the separation layer withlight so as to cause exfoliation in the separation layer and/or at theinterface; and a step for detaching the substrate from the separationlayer.

[0030] In accordance with the present invention, for example, aseparation layer having optical absorption characteristics is providedon a substrate having high reliability in device production, and thinfilm devices such as TFTs and the like are formed on the substrate.Next, although not for limitation, the thin film devices are adhered toa given transfer member, for example, with an adhesive layer, so as tocause an exfoliation phenomenon in the separation layer, which resultsin a decrease in adhering between the separation layer and thesubstrate. The substrate is detached from the thin film devices by theforce applied to the substrate. A given device with high reliability canbe thereby transferred or formed onto any transfer members.

[0031] In the present invention, either the step for adhering the thinfilm devices (the transferred layer including the thin film devices) tothe transfer member with the adhesive layer or the step for detachingthe substrate from the thin film devices may precede. When handling ofthe thin film devices (the transferred layer including the thin filmdevices) after detaching the substrate is troublesome, however, it ispreferable that the thin film devices be adhered to the transfer member,and then the substrate be detached.

[0032] When an adhesive layer for adhering the thin film devices to thetransfer member is, for example, a substance having planation, theuneven face formed on the surface of the transferred layer including thethin film devices is negligible by the planation, the adhering to thetransfer member is satisfactorily performed. The substrate may be atransparent substrate, and thus the separation layer is irradiated withthe light through the transparent substrate. The use of, for example, atransparent substrate, e.g. a quartz substrate, permits production ofthin film devices with high reliability and collective irradiation ofthe entire separation layer with the light from the rear side of thesubstrate, resulting in an improvement in the transfer efficiency.

[0033] 4. Inventions in which parts of the steps, disclosed in theabove-mentioned paragraph 3, in the method for transferring the thinfilm device will now be disclosed. These inventions are as follows:

[0034] (1) A method for transferring a transferred layer including athin film device forming on a substrate onto a transfer membercomprising: a first step for forming an amorphous silicon layer on thesubstrate; a second step for forming the transferred layer including thethin film device on the amorphous silicon layer; a third step foradhering the transferred layer including the thin film device to thetransfer member with an adhesive layer; a fourth step for irradiatingthe amorphous silicon layer with light through the substrate so as tocause exfoliation in the amorphous silicon layer and/or at the interfaceand to decrease the adhering force between the substrate and thetransferred layer; and a fifth step for detaching the substrate from theamorphous silicon layer; wherein the transferred layer formed in thesecond step includes a thin film transistor, and the thickness of theamorphous silicon layer formed in the first step is smaller than thethickness of the channel layer of the thin film transistor formed in thesecond step.

[0035] In this invention, the amorphous silicon layer is used as thelayer formed on the substrate in the first step and causes exfoliationby light irradiation. In the amorphous silicon layer as shown in FIG.39, optical energy, which is radiated in the amorphous silicon layer andwhich is required for exfoliation (referred to as ablation in FIG. 39),decreases as the thickness decreases.

[0036] The transferred layer formed in the second step includes the thinfilm transistor as a thin film device, its channel layer is formed ofsilicon, e.g., polycrystalline silicon or amorphous silicon, and thetransferred layer has a thickness of more than 25 nm, for example,approximately 50 nm. In this invention, the thickness of the amorphoussilicon as the separation layer (ablation layer) formed in the firststep is smaller than that of the channel layer of the thin filmtransistor in the transferred layer. The energy consumed in the lightirradiation step therefore decreases, and the light source can beminiaturized. Further, since optical energy by irradiation is low, thedeterioration of the thin film device is suppressed if the light leakedfrom the amorphous silicon layer is incident on the thin film device.

[0037] Now, the thickness of the amorphous silicon layer is set to 25 nmor less. As described above, the optical energy, which is radiated inthe amorphous silicon layer and which is required for exfoliation,decreases as the thickness decreases, hence the optical energy issignificantly low at this thickness. It is preferable that the thicknessof the amorphous silicon layer be in a range from 5 nm to 25 nm, morepreferably 15 nm or less, and most preferably 11 nm or less in order tofurther decrease the optical energy, which is radiated in the amorphoussilicon layer and which is required for exfoliation.

[0038] In the second step, the amorphous silicon layer is formed by alow pressure chemical vapor deposition (LPCVD) process. The amorphoussilicon layer formed by the LPCVD process has a higher adhesion comparedwith a plasma CVD process, an atmospheric pressure (AP) CVD process, oran ECR process, hence there is not much risk of failures, such asevolution of hydrogen and flaking of the film, during the formation ofthe transferred layer including the thin film device.

[0039] (2) A method for transferring a transferred layer including athin film device on a substrate onto a transfer member comprising: astep for forming a separation layer onto the substrate; a step forforming a silicon-based optical absorption layer on the separationlayer; a step for forming the transferred layer including the thin filmdevice on the silicon-based optical absorption layer; a step foradhering the transferred layer including the thin film device to thetransfer member with an adhesive layer; a step for irradiating theseparation layer with light through the substrate so as to causeexfoliation in the separation layer and/or at the interface; and a stepfor detaching the substrate from the separation layer.

[0040] In accordance with this invention, if light leaks from theseparation layer, the leaked light is absorbed in the silicon-basedoptical absorption layer before it is incident on the thin film device.No light is therefore incident on the thin film device, hence the thinfilm device is prevented from characteristic deterioration due to theincident light. The transferred layer including the thin film device canbe formed on the silicon-based optical absorption layer. Metalliccontamination will therefore not occur as in the case forming thetransferred layer onto a metallic layer reflecting light, and the thinfilm device can be formed by an established thin film depositiontechnology.

[0041] The separation layer and the optical absorption layer are formedof amorphous silicon, and a step for providing a silicon-basedintervening layer between the separation layer and the opticalabsorption layer. As shown in FIG. 39, the amorphous silicon layer,which absorbs the incident light and separates when the energy of theabsorbed light reaches a given value, is used as the separation layerand the silicon-based optical absorption layer. As the intervening layerfor separating the two amorphous silicon layers, a silicon compound, forexample, silicon oxide, is used.

[0042] (3) A method for transferring a transferred layer including athin film device on a substrate onto a transfer member comprising: afirst step for forming a separation layer on the substrate; a secondstep for forming the transferred layer including the thin film device onthe separation layer; a third step for adhering the transferred layerincluding the thin film device to the transfer member with an adhesivelayer; a fourth step for irradiating the separation layer with lightthrough the substrate so as to cause exfoliation in the separation layerand/or at the interface; and a fifth step for detaching the substratefrom the separation layer; wherein, in the fourth step, the stress,acting on the upper layers above the separation layer in the exfoliationin the separation layer and/or at the interface, is absorbed by theproof stress of the upper layers above the separation layer to preventthe deformation or breakage of the upper layers above the separationlayer.

[0043] In the fourth step, the substances in the separation layer areoptically or thermally excited by the incident light to cut bonds ofatoms or molecules on the surface and in the interior and liberate themolecules and atoms to the exterior. This phenomenon is observed asphase transition, such as melting or evaporation, of the partial orentire substances in the separation layer. A stress acts on the upperlayers above the separation layer as the molecules or atoms arereleased. The stress is, however, absorbed by the proof stress of theupper layers above the separation layer so as to prevent deformation orbreakage of the upper layers above the separation layer.

[0044] The materials and/or thicknesses of the upper layers above theseparation layer may be designed in view of such a proof stress. Forexample, one or more among the thickness of the adhesive layer, thethickness of the transferred layer, the material, and the thickness ofthe transfer member is designed in view of the proof stress.

[0045] Before performing the fourth step, the method further includes astep for forming a reinforcing layer for ensuring the proof stress atany position among the upper layers above the separation layer. In thisinvention, if the proof stress is not ensured only by the minimumconfiguration of the upper layers above the separation layer, consistingof the adhesive layer, the transferred layer, and the transfer member,deformation and breakage of the thin film device is prevented by addingthe reinforcing layer.

[0046] (4) A method for transferring a transferred layer including athin film device on a substrate onto a transfer member comprising: afirst step for forming a separation layer on the substrate; a secondstep for forming the transferred layer including the thin film device onthe separation layer; a third step for adhering the transferred layerincluding the thin film device to the transfer member with an adhesivelayer; a fourth step for irradiating the separation layer with lightthrough the substrate so as to cause exfoliation in the separation layerand/or at the interface; and a fifth step for detaching the substratefrom the separation layer; wherein, the fourth step includes sequentialscanning of beams for locally irradiating the separation layer, suchthat a region irradiated by the N-th beam (wherein N is an integer of 1or more) does not overlap with other irradiated regions.

[0047] In the fourth step, beams, such as spot beams or line beams, forlocally irradiating the separation layer are intermittently scanned sothat substantially all the surface of the separation layer is irradiatedwith light. The beam scanning is achieved by relative movement betweenthe substrate provided with the separation layer and the beam source orits optical system, and irradiation may be continued or discontinuedduring the relative movement. In this invention, the intermittent beamscanning is performed so that the adjacent beam-irradiated regions donot overlap with each other.

[0048] If the beam-irradiated regions overlap, the region may beirradiated with an excessive amount of light which will causeexfoliation in the separation layer or at the interface. It is clarifiedby analysis by the present inventor that an excessive amount of lightpartially leaks, is incident on the thin film device, and causes thedeterioration of electrical characteristics and the like of the thinfilm device.

[0049] In the present invention, the separation layer is irradiated withsuch an excessive amount of light, hence the original characteristics ofthe thin film device are maintained after the thin film device istransferred onto the transfer member. A zone between individualbeam-irradiated regions may be a low irradiation zone in which light isincident during the relative movement or a non-irradiation zone in whichno light is incident during the relative movement. Exfoliation does notoccur in the low irradiation zone or non-irradiation zone, the adhesionbetween the separation layer and the substrate can be remarkablyreduced.

[0050] In the following two inventions, each beam for preventing orsuppressing the characteristic deterioration of the thin film device isdetermined in different views from the invention in paragraph (4).

[0051] In the fourth step of the first invention, beams are sequentiallyscanned to irradiate locally the separation layer, each beam has a flatpeak region having the maximum optical intensity in the center, and aregion irradiated by the N-th beam (wherein N is an integer of 1 ormore) does not overlap with other irradiated regions.

[0052] In the fourth step of the other invention, beams are sequentiallyscanned to irradiate locally the separation layer, each beam has themaximum optical intensity in the central region, and an effective regionirradiated by the N-th beam (wherein N is an integer of 1 or more)having an intensity, which is 90% or more of the maximum intensity, doesnot overlap with the other effective regions irradiated by other beamscanning.

[0053] Since individual beams are scanned so that the flat peaks ofindividual beams or the effective regions having intensities which are90% or more of the maximum intensity do not overlap with each other, twobeams are continuously scanned in the same region in the separationlayer.

[0054] The total irradiated beam (sum of the optical intensity×time) inthe same region is lower than that when the flat peak region or theeffective region having intensities which are 90% or more of the maximumintensity is set at the same position in the two consecutively scannedbeams. As a result, the separation layer may separate after the secondscanning in some regions, and this case does not correspond to theexcessive irradiation. In another case, even if the separation layerseparates in the first scanning, the intensity of the light incident onthe thin film device in the second scanning is decreased, hence thedeterioration of the electric characteristics of the thin film devicecan be prevented or reduced.

[0055] In the thin film device formed on a given substrate by a transfertechnology of the thin film device (the thin film structure) inaccordance with the present invention, the deterioration of variouscharacteristics can be prevented or reduced by improving the irradiatingstep for exfoliating the separation layer.

[0056] When the thin film device is a thin film transistor (TFT), theimproved irradiation step for exfoliating the separation layer canprevent the breakdown of the TFT due to a decreased on-current flow andan increased off-current flow in the channel layer of the TFT damaged bythe incident light.

[0057] 5. Further, the following inventions are disclosed in connectionwith the above-mentioned inventions.

[0058] A step for removing the separation layer adhered to the transfermember is provided for completely removing the unnecessary separationlayer.

[0059] The transfer member is a transparent substrate. For example,inexpensive substrates such as a soda glass substrate and flexibletransparent plastic films may be used as the transfer member. When themaximum temperature of the transfer member during the formation is Tmax,the transfer member is composed of a material having a glass transitionpoint (Tg) or softening point which is lower than Tmax.

[0060] Although such inexpensive glass substrates etc. have not beenused because they are not resistive to the maximum temperature of theconventional device production processes, they can be used in thepresent invention without restriction.

[0061] The glass transition point (Tg) or softening point of thetransfer member is lower than the maximum temperature in the process forforming the thin film device. The upper limit of the glass transitionpoint (Tg) or softening point is defined. The transfer member iscomposed of a synthetic resin or a glass material. For example, when thethin film device is transferred onto a flexible synthetic resin platesuch as a plastic film, excellent characteristics which are notobtainable in a glass substrate with high rigidity can be achieved. Whenthe present invention is applied to a liquid crystal device, a flexiblelightweight display device which is resistive to falling can beachieved.

[0062] Also, a thin film integrated circuit such as a single-chipmicrocomputer including TFTs can be formed by transferring the TFTs on asynthetic resin substrate by the above-mentioned transferring method.

[0063] An inexpensive substrate such as a soda-glass substrate can alsobe used as the transfer member. A soda-glass substrate is inexpensiveand thus has economical advantages. Since alkaline components aredissolved from the soda-glass substrate during annealing of the TFTproduction, it has been difficult to apply active matrix liquid crystaldisplay devices. In accordance with the present invention, however,since a completed thin film device is transferred, the above-mentionedproblems caused by the annealing will not occur. Accordingly, substrateshaving problems in the prior art technologies, such as a soda-glasssubstrate, can be used in the field of active matrix liquid crystaldisplay devices.

[0064] The substrate has thermal resistivity: The thin film device canbe annealed at a high temperature in the production process, and theresulting thin film device has high reliability and high performance.

[0065] The substrate has a transmittance of 10% or more for the 310 nmlight: The transparent substrate can supply optical energy sufficient toablation in the separation layer.

[0066] When the maximum temperature in the formation of the transferredlayer is Tmax, the substrate is composed of a material having adistortion point of Tmax or more: The thin film device can be treated ata high temperature in the production process, and the resulting thinfilm device has high reliability and high performance.

[0067] The separation layer may be composed of amorphous silicon: Theamorphous silicon can absorb light, can be easily produced, and has ahighly practical use.

[0068] The amorphous silicon contains 2 atomic percent or more ofhydrogen (H): When the amorphous silicon containing hydrogen is used,hydrogen is released by light irradiation, and an internal pressureoccurs in the separation layer to promote exfoliation in the separationlayer. The amorphous silicon may contain 10 atomic percent or more ofhydrogen (H). The exfoliation in the separation layer is furtheraccelerated by the increased hydrogen content.

[0069] Alternatively, the separation layer may be composed of siliconnitride: When using silicon nitride as a separation layer, nitrogen isreleased by light irradiation to promote exfoliation in the separationlayer.

[0070] Alternatively, the separation layer may be composed of ahydrogen-containing alloy: When using a hydrogen-containing alloy,hydrogen is released by light irradiation to promote exfoliation in theseparation layer.

[0071] Alternatively, the separation layer may be composed of anitrogen-containing alloy: When using a nitrogen-containing alloy,nitrogen is released by light irradiation to promote exfoliation in theseparation layer.

[0072] The separation layer may be composed of a multi-layered film: Theseparation layer is therefore not limited to a single-layered film. Themulti-layered film is composed of an amorphous silicon film and ametallic film formed thereon.

[0073] The separation layer may be composed of at least one materialselected from the group consisting of ceramics, metals, and organicpolymers. Usable metals include, for example, hydrogen containing alloysand nitrogen containing alloys. As in amorphous silicon, exfoliation inthe separation layer is accelerated by the evolution of gaseous hydrogenor nitrogen by light irradiation.

[0074] The light is laser light. Laser light is coherent light and issuitable for causing exfoliation in the separation layer. The laserlight has a wavelength of 100 nm to 350 nm. The short-wave, high energylaser light results in effective exfoliation in the separation layer. Anexample of such a laser is an excimer laser. The excimer laser is a gaslaser which is capable of outputting laser light with high energy, andfour typical types of laser light can be output (XeF=351 nm, XeCl=308nm, KrF=248 nm, ArF=193 nm) by combinations of rare gasses (Ar, Kr, andXe) and halogen gasses (F₂ and HCl) as laser media. By excimer laserirradiation, direct scission of molecular adheres and gas evolution willoccur in the separation layer provided on the substrate, without thermaleffects.

[0075] The laser light may have a wavelength of 350 nm to 1,200 nm. Forthe purpose of imparting exfoliation characteristics to the separationlayer by changes, such as gas evolution, vaporization, and sublimation,laser light having a wavelength of 350 nm to 1,200 nm can also be used.

[0076] The thin film device may be a thin film transistor (TFT). The TFTmay be a CMOS-type TFT.

[0077] A high-performance TFT can be transferred (formed) on a giventransfer member without restriction. Various electronic circuits cantherefore be mounted on the transfer member. Accordingly, by theabove-mentioned inventions, a thin film integrated circuit deviceincluding the thin film device transferred onto the transfer member isachieved. Also, a liquid crystal display device including an activematrix substrate, which is produced by the transfer of the thin filmtransistors in the pixel region, is achieved, wherein the pixel regionincludes a matrix of thin film transistors and pixel electrodes eachconnected to one end of each thin film transistor.

BRIEF DESCRIPTION OF DRAWINGS

[0078] FIGS. 1 to 8 are cross-sectional views of steps in a firstembodiment of an exfoliating method in accordance with the presentinvention.

[0079] FIGS. 9 to 16 are cross-sectional views of steps in a secondembodiment of an exfoliating method in accordance with the presentinvention.

[0080] FIGS. 17 to 22 are cross-sectional views of steps in a thirdembodiment of a method for transferring a thin film device in accordancewith the present invention.

[0081]FIG. 23 is a graph illustrating a change in the transmittance of afirst substrate (a substrate 100 in FIG. 17) to the wavelength of laserlight.

[0082] FIGS. 24 to 34 are cross-sectional views of steps in a fourthembodiment of a method for transferring a thin film device in accordancewith the present invention.

[0083] FIGS. 35(a) and 35(b) are isometric views of a microcomputerproduced in accordance with the present invention.

[0084]FIG. 36 is a schematic view illustrating a configuration of aliquid crystal display device.

[0085]FIG. 37 is a schematic view illustrating a configuration of themain section in a liquid crystal display device.

[0086]FIG. 38 is a cross-sectional view of another embodiment of amethod for transferring a thin film device in accordance with thepresent invention.

[0087]FIG. 39 is a graph of a relationship between optical energyabsorbed in the separation layer and the thickness of the separationlayer, for illustrating ablation in the separation layer which iscomposed of amorphous silicon.

[0088]FIG. 40 is a cross-sectional view of another embodiment in whichan amorphous silicon layer as an optical absorption layer is formed onan amorphous silicon layer as a separation layer with a silicon-basedintervening layer therebetween.

[0089]FIG. 41 is a cross-sectional view of another embodiment in which asilicon-based optical absorption layer composed of a material which isdifferent from that of a separation layer is formed on the separationlayer.

[0090] FIGS. 42(A) to 42(E) are cross-sectional views of anotherembodiment in which a reinforcing layer is provided to preventdeformation or breakage of a thin film device during exfoliation of aseparation layer.

[0091]FIG. 43 is a schematic view illustrating a scanning operation ofbeams onto a separation layer in a step in a method for transferring athin film device in accordance with the present invention.

[0092]FIG. 44 is a plan view illustrating beam scanning in FIG. 42.

[0093]FIG. 45 is a schematic view illustrating another embodiment of ascanning operation of beams onto a separation layer in a step in amethod for transferring a thin film device in accordance with thepresent invention.

[0094]FIG. 46 is a graph of characteristic curves illustrating anintensity distribution of beams used in the beam scanning shown in FIG.45.

[0095]FIG. 47 is a graph of characteristic curves illustrating anotherintensity distribution of beams used in the beam scanning shown in FIG.45.

BEST MODE FOR CARRYING OUT THE INVENTION

[0096] Embodiments of the exfoliating method in accordance with thepresent invention will now be described in detail with reference to theattached drawings.

[0097] [First Embodiment]

[0098] FIGS. 1 to 8 are cross-sectional views of steps in a firstembodiment of an exfoliating method in accordance with the presentinvention. These steps in the exfoliating method (transferring method)in accordance with the present invention will now be described.

[0099] [1] As shown in FIG. 1, a separation layer (optical absorptionlayer) 2 is formed on one side (an inner surface 11 forming exfoliation)of a substrate 1. It is preferable that the substrate 1 has transparencyto allow indent light 7 to pass through from the side of the substrate1. The transmittance of the incident light 7 is preferably 10% or more,and more preferably 50% or more. A significantly low transmittancecauses a large loss of the incident light 7, hence a larger amount oflight is required for exfoliation of the separation layer 2.

[0100] The substrate 1 is preferably composed of a material with highreliability, and particularly composed of a heat-resistant material.When forming a transferred layer 4 and an interlayer 3 as describedlater, a process temperature will increase depending on the types orformation processes (for example, from 350° C. to 1,000° C.) In such acase, if the substrate 1 has excellent heat resistance, the conditionsfor forming the films, such as a temperature, are widely changed in theformation of the transferred layer 4 and the like on the substrate 1.

[0101] When the maximum temperature in the formation of the transferredlayer 4 is Tmax, it is preferable that the substrate 1 be composed of amaterial having a distortion point of Tmax. That is, it is preferablethat the material for the substrate 1 has a distortion point of 350° C.or more, and more preferably 500° C. or more. Examples of such materialsinclude heat-resistant glass, such as quartz glass, soda glass, Corning7059, and OA-2 made by Nippon Electric Glass Co., Ltd.

[0102] When the process temperature is decreased in the formation of theseparation layer 2, interlayer 3, and transferred layer 4, the substrate1 can be composed of an inexpensive glass material or synthetic resinhaving a lower melting point.

[0103] Although the thickness of the substrate 1 is not limited, it ispreferable that the thickness be generally about 0.1 to 5.0 mm, and morepreferably 0.5 to 1.5 mm. A remarkably small thickness of the substrate1 causes decreased mechanical strength, whereas an excessively largethickness causes a large loss of the incident light 7 if the substrate 1has a low transmittance. When the substrate 1 has a high transmittancefor the incident light 7, the thickness may be larger than theabove-mentioned upper limit.

[0104] It is preferable that the thickness of the substrate 1 at theportion for forming the separation layer be uniform for achievinguniform irradiation by the incident light 7. The inner surface 11 forexfoliation and the light-incident surface 12 of the substrate are notlimited to the planar form, and may also be curved. In the presentinvention, the substrate 1 is not removed by etching etc., but thesubstrate 1 is removed by exfoliation in the separation layer 2 providedbetween the substrate 1 and the transferred layer 4, hence the operationis easy, and the substrate 1 has high selectivity, for example, arelatively high thickness.

[0105] The separation layer 2 will now be described. The separationlayer 2 absorbs the incident light 7 to cause exfoliation in the layerand/or at an interface 2 a or 2 b (hereinafter referred to as “internalexfoliation” and “interfacial exfoliation”). Irradiation by the incidentlight 7 causes an elimination or reduction of the adhering force betweenatoms or molecules in the constituent substance of the separation layer2, that is, ablation, and internal and/or interfacial exfoliation willoccur as a result. Further, in some cases, gas will be released from theseparation layer 2 by the incident light 7, resulting in theexfoliation. Consequently, there are two exfoliation mechanisms, thatis, releasing components contained in the separation layer 2 as gas, andinstantaneous vaporization of the separation layer 2 by absorption ofthe light followed by release of the vapor.

[0106] Examples of the composition for the separation layer 2 are thefollowing (1) to (6):

[0107] (1) Amorphous Silicon (a-Si):

[0108] Amorphous silicon may contain hydrogen (H). In this case, it ispreferable that the hydrogen content be approximately 2 atomic percentor more, and more preferably 2 to 20 atomic percent. When a given amountof hydrogen is contained, hydrogen is released by irradiation of theincident light 7, and an internal pressure, which will act as a forcefor delaminating the upper and lower thin films, occurs in theseparation layer 2. The hydrogen content in the amorphous silicon can becontrolled by determining the film forming conditions, for example, thegas composition, gas pressures, gas atmospheres, gas flow rates,temperature, substrate temperature, and input power in the CVD process.

[0109] (2) Oxide Ceramics, Dielectrics (Ferroelectrics) andSemiconductors, such as Silicon Oxides and Silicates, Titanium Oxidesand Titanates, Zirconium Oxide and Zirconates, and Lanthanum Oxide andLanthanates:

[0110] Examples of silicon oxides include SiO, SiO₂, and Si₃O₂, andexamples of silicates include K₂SiO₃, Li₂SiO₃, CaSiO₃, ZrSiO₄, andNa₂SiO₃. Examples of titanium oxides include TiO, Ti₂O₃, and TiO, andexamples of titanates include BaTiO₄, BaTiO₃, Ba₂Ti₉O₂₀, BaTi₅O₁₁,CaTiO₃, SrTiO₃, PbTiO₃, MgTiO₃, ZrTiO₂, SnTiO₄, Al₂TiO₅, and FeTiO₃.Examples of zirconium oxides include ZrO₂, and examples of zirconatesinclude BaZrO₃, ZrSiO₄, PbZrO₃, MgZrO₃, and K₂ZrO₃.

[0111] (3) Ceramics and Dielectrics (Ferroelectrics), such as PZT, PLZT,PLLZT and PBZT:

[0112] (4) Nitride Ceramics, such as Silicon Nitride, Aluminum Nitride,and Titanium Nitride:

[0113] (5) Organic Polymers:

[0114] Usable organic polymers have linkages (which are cut byirradiation of the incident light 7), such as —CH₂—, —CO— (ketone),—CONH— (amido), —NH— (imido), —COO— (ester), —N═N— (azo), and —CH═N—(isocyano). In particular, any organic polymers having large numbers ofsuch linkages can be used. The organic polymers may have aromatichydrocarbon (one or more benzene ring or fused ring) in the chemicalformulae. Examples of the organic polymers include polyolefins, such aspolyethylene, and polypropylene; polyimides; polyamides; polyesters;polymethyl methacrylate (PMMA); polyphenylene sulfide (PPS); polyethersulfone (PES); and epoxy resins.

[0115] (6) Metals:

[0116] Examples of metals include Al, Li, Ti, Mn, In, Sn, Y, La, Ce, Nd,Pr, Gd, and Sm; and alloys containing at least one of these metals.

[0117] The thickness of the separation layer 2 depends on variousconditions, such as the purpose for exfoliation, the composition of theseparation layer 2, the layer configuration, and the method for formingthe layer, and has a thickness of generally about 1 nm to 20 μm,preferably about 10 nm to 2 μm, and more preferably about 40 nm to 1 μm.A significantly small thickness requires a larger amount of incidentlight 7 in order to secure excellent exfoliation characteristics of theseparation layer 2, and an operational time for removing the separationlayer 2 in the succeeding step. It is preferable that the thickness ofthe separation layer 2 be as uniform as possible.

[0118] The method for forming the separation layer 2 is not limited, andis determined depending on several conditions, such as the filmcomposition and thickness. Examples of the methods include vapor phasedeposition processes, such as CVD (including MOCVD, low pressure CVD,ECR-CVD), evaporation, molecular beam (MB) evaporation, sputtering,ion-plating, and PVD; plating processes, such as electro-plating,dip-plating (dipping), and electroless-plating; coating process, such asa Langmuir-Blodgett process, spin-coating process, spray-coatingprocess, and roll-coating process; printing processes; transferprocesses; ink-jet processes; and powder-jet processes. A combination ofthese processes may also be used. For example, when the separation layer2 is composed of amorphous silicon (a-Si), it is preferable that thelayer be formed by a low pressure CVD process or a plasma CVD process.Alternatively, when the separation layer 2 is composed of a ceramic by asol-gel process, or an organic polymer, it is preferable that the layerbe formed by a coating process, and particularly a spin-coating process.The separation layer 2 may be formed by two or more steps (for example,a layer-forming step and an annealing step).

[0119] [2] As shown in FIG. 2, an interlayer (underlying layer) 3 isformed on the separation layer 2.

[0120] The interlayer 3 is formed for various purposes, for example, asa protective layer which physically and chemically protects thetransferred layer 4 during production and use, an insulating layer, aconductive layer, a shading layer for the incident light 7, a barrierlayer prohibiting migration of components to or from the transferredlayer 4, and a reflection layer.

[0121] The composition of the interlayer 3 is determined by the purpose.For example, the interlayer 3, formed between the separation layer 2composed of amorphous silicon and the transferred layer 4 including athin film transistor, is composed of silicon oxides such as SiO₂.Alternatively, the interlayer 3, formed between the separation layer 2and the transferred layer 4 including PZT, is composed of a metal, suchas Pt, Au, W, Ta, Mo, Al, Cr, or Ti, or an alloy primarily containingsuch a metal. The thickness of the interlayer 3 is determined inresponse to the purpose and functions, and ranges generally from about10 nm to 5 μm, and preferably about 40 nm to 1 μm. The interlayer 3 maybe formed by the same method as for the separation layer 2. Theinterlayer 3 may be formed by two or more steps.

[0122] The interlayer 3 may include two or more layers having the samecomposition or different compositions. In the present invention, thetransferred layer 4 may be formed directly on the separation layer 2without forming the interlayer 3.

[0123] [3] As shown in FIG. 3, a transferred layer (detached member) isformed on the interlayer 3. The transferred layer 4 will be transferredonto a transfer member 6 later, and is formed by the same method as inthe separation layer 2.

[0124] The purpose for forming the transferred layer 4, and type, shape,structure, composition, and physical and chemical characteristics of thetransferred layer 4 are not limited, and it is preferable that thetransferred layer 4 be a thin film, and particularly a functional thinfilm or thin film device. Examples of functional thin films and thinfilm devices include thin film transistors; thin film diodes; other thinfilm semiconductor devices; electrodes (e.g. transparent electrodes suchas ITO and mesa films); photovoltaic devices used in solar batteries andimage sensors; switching devices; memories; actuators such aspiezoelectric devices; micromirrors (piezoelectric thin film ceramics);recording media such as magnetic recording media, magneto-opticalrecording media, and optical recording media; magnetic recording thinfilm heads, coils, inductors and thin film high permeability materials,and micro-magnetic devices composed of combinations thereof; opticalthin films such as filters, reflection films, dichroic mirrors, andpolarizers; semiconductor thin films; superconducting thin films, e.g.YBCO thin films; magnetic thin films; and multi-layered thin films, suchas metallic multi-layered thin films, metallic-ceramic multi-layeredthin films, metallic multi-layered semiconductor thin films, ceramicmulti-layered semiconductor thin films, and multi-layered thin filmsincluding organic layers and other layers. Among them, application tothin film devices, micro-magnetic devices, three-dimensionalmicro-articles, actuators, and micromirrors is useful.

[0125] Such a functional thin film or thin film device is formed by arelatively high process temperature because of the method for formingit. The substrate 1 must therefore be a highly reliable material whichis resistant to the high process temperature, as described above.

[0126] The transferred layer 4 may be a single layer or a composite of aplurality of layers. The transferred layer, such as a thin filmtransistor, may have a given pattern. The formation (deposition) andpatterning of the transferred layer 4 is performed by a predeterminedprocess. The transferred layer 4 is generally formed by a plurality ofsteps.

[0127] The transferred layer 4 including thin film transistors is formedby, for example, the methods described in Japanese Patent PublicationNo. 2-50630, and H. Ohsima et al.: International Symposium Digest ofTechnical Papers SID 1983 “B/W and Color LC Video Display Addressed byPoly Si TFTs”.

[0128] The thickness of the transferred layer 4 is not limited, and isdetermined in response to various factors, e.g. purpose, function,composition, and characteristics. When the transferred layer 4 includesthin film transistors, its total thickness is preferably 0.5 to 200 μm,and more preferably 0.5 to 10 μm. In the case of other thin films, thepreferable thickness has a wider thickness range, for example, 50 nm to1,000 μm.

[0129] The transferred layer 4 is not limited to the above-describedthin films, and may be thick films, such as coating films and sheets,and transfer materials or separable materials, such as powder, notforming films or layers.

[0130] [4] As shown in FIG. 4, an adhesive layer 5 is formed on thetransferred layer (a detached member) 4, and a transfer member 6 isadhered with the adhesive layer 5. Examples of preferable adhesivesforming the adhesive layer 5 include curable adhesives, for example,reactive curing adhesives, heat-hardening adhesives, photo-settingadhesives such as UV-curing adhesives, and anaerobic curing adhesives.Examples of types of adhesives include epoxys, acrylates, and silicones.The adhesive layer 5 is formed by, for example, a coating process.

[0131] When using a curable adhesive, for example, the curable adhesiveis applied onto the transferred layer 4, the transfer member 6 isadhered thereon, and then the curable adhesive is cured by a method inresponse to characteristics of the curable adhesive to adhere thetransferred layer 4 to the transfer member 6. When using a photo-settingadhesive, it is preferable that a transparent transfer member 6 beplaced on the uncured adhesive layer 5, and then the substrate 1 and thetransfer member 6 be illuminated with light for curing from both sidesin order to secure the curing of the adhesive.

[0132] Regardless of the drawings, the adhesive layer 5 may be formed onthe transfer member 6 and then the transferred layer 4 may be adheredthereto. Further, the above-mentioned interlayer may be provided betweenthe transferred layer 4 and the adhesive layer 5. When the transfermember 6 has an adhering function, the formation of the adhesive layer 5may be omitted.

[0133] Examples of the transfer member 6 include substrates (plates),and particularly transparent substrates, although they are not limitedto these substrates. Such substrates may be planar or curved. Thetransfer member 6 may have inferior characteristics including heatresistance and corrosion resistance to those of the substrate 1,because, in the present invention, the transferred layer 4 is formed onthe substrate 1, and the transferred layer 4 is transferred to thetransfer member 6, wherein characteristics required for the transfermember 6 are independent of the conditions, such as temperature, in theformation of the transferred layer 4.

[0134] Accordingly, when the maximum temperature in the formation of thetransferred layer 4 is Tmax, the transfer member 6 can be formed of amaterial having a glass transition point (Tg) or softening point of Tmaxor less. For example, the transfer member 6 is composed of a materialhaving a glass transition point (Tg) or softening point of 800° C. orless, preferably 500° C. or less and more preferably 320° C. or less.

[0135] It is preferable that the transfer member 6 has a given level ofrigidity (mechanical strength), but it may have flexibility orelasticity. Examples of materials for such a transfer member 6 include awide variety of synthetic resins and glass materials, and preferablysynthetic resins and inexpensive glass materials (with low meltingpoints).

[0136] Examples of synthetic resins include both thermoplastic resinsand thermosetting resins, such as polyolefins, e.g. polyethylene,polypropylene, ethylene-propylene copolymers, and ethylene-vinyl acetatecopolymers (EVAs); cyclic polyolefins; modified polyolefins; polyvinylchloride; polyvinylidene chloride; polystyrene; polyamides;polyamide-imides; polycarbonates; poly-(4-methylpentene-1); ionomers;acrylic resins; polymethyl methacrylate (PMMA);acrylonitrile-butadiene-styrene copolymers (ABS resins);acrylonitrile-styrene copolymers (AS resins); butadiene-styrenecopolymers; polyoxymethylene; polyvinyl alcohol (PVA); ethylene-vinylalcohol copolymers (EVOHs); polyesters, e.g. polyethylene terephthalate(PET), polybutylene terephthalate (PBT), and polycyclohexaneterephthalate (PCT); polyethers; polyether-ketones (PEKs);polyether-ether-ketone (PEEKs); polyether-imides; polyacetals (POMs);polyphenylene oxides; modified polyphenylene oxides; polysulfones;polyphenylene sulfide (PPS); polyether sulfones (PESs); polyarylates;aromatic polyesters (liquid crystal polymers); polytetrafluoroethylene;polyvinylidene fluoride; other fluorine resins; thermoplasticelastomers, e.g. styrene-, polyolefin-, polyvinyl chloride-,polyurethane-, polyester-, polyamide-, polybutadiene-,trans-polyisoprene-, fluorine rubber-, and chlorinatedpolyethylene-type; epoxy resins; phenol resins; urea resins; melamineresins; unsaturated polyesters; silicone resins; and polyurethanes; andcopolymers, blends, and polymer alloys essentially consisting of thesesynthetic resins. One or more of these synthetic resins may be used, forexample, as a composite consisting of at least two layers.

[0137] Examples of usable glasses include silicate glass (quartz glass),alkaline silicate glass, soda-lime glass, lead (alkaline) glass, bariumglass, and borosilicate glass. All the types of glass other thansilicate glass have lower boiling points than that of silicate glass,can be readily formed and shaped, and are inexpensive.

[0138] When a synthetic resin is used, a large transfer member 6provided with a complicated shape, such as a curved surface orunevenness, can be readily formed with low material and productioncosts. A large, inexpensive device, for example, a liquid crystaldisplay, can therefore be readily formed.

[0139] The transfer member 6 may function as an independent device, suchas a liquid crystal cell, or as a part of a device, for example, a colorfilter, an electrode layer, a dielectric layer, an insulating layer, anda semiconductor device. Further, the transfer member 6 may be composedof metal, ceramic, stone, wood, or paper. Alternatively, it may be asurface of a given article (the surface of a watch, clock, airconditioner, or print board), or a surface of a given structure, such asa wall, pillar, post, beam, ceiling, or window glass.

[0140] [5] As shown in FIG. 5, the rear side of the substrate 1 (theside 12 of the incident light) is irradiated with the incident light 7.The incident light 7 passes though the substrate 1 and enters theseparation layer 2 through the interface 2 a. As shown in FIG. 6 or FIG.7, internal and/or interfacial exfoliation occurs in the separationlayer and the adhering force is reduced or eliminated. When separatingthe substrate 1 from the transfer member 6, the transferred layer 4 isdetached from the substrate 1 and transferred to the transfer member 6.

[0141]FIG. 6 shows a state of the internal exfoliation in the separationlayer 2, and FIG. 7 shows a state of the interfacial exfoliation at theinterface 2 a on the separation layer 2. The occurrence of the internaland/or interfacial exfoliation presumes that ablation of theconstituents in the separation layer 2 occurs, that gas retained in theseparation layer 2 is released, and that phase transition such asmelting or vaporization occurs immediately after the light irradiation.

[0142] The word “ablation” means that solid components (the constituentsof the separation layer 2), which absorbed the incident light, arephotochemically and thermally excited and atoms or molecules in thesolid components are released by the chain scission. The ablation isobserved as phase transition such as melting or vaporization in thepartial or entire constituents of the separation layer 2. Also, finefoaming may be formed by the phase transition, resulting in a decreasedadhering force. The internal and/or interfacial exfoliation of theseparation layer 2 depends on the composition of the separation layer 2and other factors, for example, the type, wavelength, intensity and,range of the incident light 7.

[0143] Any type of incident light 7, which causes internal and/orinterfacial exfoliation of the separation layer 2, can be used, forexample, X-rays, ultraviolet rays, visible rays, infrared rays (heatrays), laser beams, milli-waves, micro-waves, electron rays, andradiations (α-rays, β-rays, and γ-rays). Among them, laser beams arepreferable because they can easily cause exfoliation (ablation) of theseparation layer 2.

[0144] Examples of lasers generating the laser beams include gas lasersand solid lasers (semiconductor lasers), and excimer lasers, Nd-YAGlasers, Ar lasers, CO₂ lasers, CO lasers, and He—Ne lasers may bepreferably used. Among them excimer lasers are more preferably used. Theexcimer lasers output high energy laser beams in a shorter wavelengthrange which cause ablation in the separation layer 2 within asignificantly shorter time. The separation layer 2 is therefore cleavedsubstantially without the temperature rise, and thus withoutdeterioration or damage of the adjacent or adjoining interlayer 3,transferred layer 4, and substrate 1.

[0145] If the ablation of the separation layer 2 is dependent on thewavelength of the incident light, it is preferable that the wavelengthof the incident laser beam be approximately 100 nm to 350 nm.

[0146] When exfoliating the separation layer 2 by means of phasetransition, for example, gas evolution, vaporization, or sublimation, itis preferable that the wavelength of the incident laser beam beapproximately 350 nm to 1,200 nm.

[0147] Preferably, the energy density of the incident light, andparticularly of the excimer lasers ranges from approximately 10 to 5,000mJ/cm² and more preferably approximately 100 to 1,000 mJ/cm². Theirradiation time preferably ranges from 1 to 1,000 nsec., and morepreferably from 10 to 200 nsec. At an energy density or irradiation timewhich is lower than the lower limit, satisfactory ablation will notoccur, whereas at an energy density or irradiation time which is higherthan the upper limit, the transferred layer 4 is adversely affected bythe incident light passing through the separation layer 2 and interlayer3.

[0148] It is preferable that the incident light 7 including laser beamswith a uniform intensity be incident on the separation layer. Theincident light 7 may be incident on the separation layer 2 from thedirection perpendicular to the separation layer 2 or from a directionshifted by a given angle from the perpendicular direction.

[0149] When the separation layer 2 has an area which is larger than thearea per scanning of the incident light, the entire separation layer 2may be irradiated with several scans of incident light. The sameposition may be irradiated two or more times. The same position ordifferent positions may be irradiated with different types and/orwavelengths of incident (laser) light beams two or more times.

[0150] [6]As shown in FIG. 8, the separation layer 2 remaining on theinterlayer 3 is removed by, for example, washing, etching, ashing orpolishing, or a combination of these methods. Also, the separation layer2 remaining on the substrate 1 is removed in the internal separation ofthe separation layer 2, as shown in FIG. 6.

[0151] When the substrate 1 is composed of an expensive or rarematerial, such as quartz glass, the substrate 1 is preferably reused. Inother words, the present invention is applicable to the substrate to bereused, hence it is useful.

[0152] The transfer of the transferred layer 4 to the transfer member 6is completed by the above-mentioned steps. Removal of the interlayer 3adjoining the transferred layer 4 or formation of additional layers maybe employed.

[0153] In the present invention, the transferred layer 4 is not directlyseparated as the detached member, but the separation layer 2 adhered tothe transferred layer 4 is exfoliated, hence uniform exfoliation ortransfer is easily, securely, and uniformly achieved regardless ofcharacteristics and conditions of the detached member (transferred layer4). Since the detached member (transferred layer 4) is not damaged, itcan maintain high reliability.

[0154] In the embodiment shown in the drawings, a method fortransferring the transferred layer 4 onto the transfer member 6 isdescribed. The exfoliating method in accordance with the presentinvention does not always include such transfer. In this case, adetached member is used instead of the transferred layer 4. The detachedmember may be either a layered material or non-layered material.

[0155] The detached member may be used for various purposes, forexample, removal (trimming) of unnecessary portions of the thin film(particularly functional thin film), removal of attached members, suchas dust, oxides, heavy metals, and carbon, and recycling of thesubstrate used in the exfoliation method.

[0156] The transfer member 6 may be composed of a material having quitedifferent properties from that of the substrate 1 (regardless oftransparency), for example, various types of metal, ceramic, carbon,paper, and rubber, as well as the above-described materials. When thetransfer member 6 does not permit or is not suitable for directformation of the transferred layer 4, the present invention can beusefully applied.

[0157] In the embodiment shown in the drawings, the incident light 7 isincident on the substrate 1, however, it may be incident on the sideaway from the substrate 1 when the adhered material (detached member) isremoved or when the transferred layer 4 is not adversely affected byirradiation with the incident light.

[0158] Although the exfoliating method in accordance with the presentinvention has been described, the present invention is not limited tothe description.

[0159] For example, the surface of the separation layer 2 may beirradiated with the incident light to form a given pattern such that thetransferred layer 4 is cleaved or transferred based on the pattern (afirst method). In this case, in the above-mentioned step [5], the side12 of the incident light of the substrate 1 is masked in response to thepattern before irradiation of the incident light 7, or the positionsirradiated with the incident light 7 are accurately controlled.

[0160] The separation layer 2 having a given pattern may be formedinstead of forming the separation layer 2 on the entire face 11 of thesubstrate 1 (a second method). In this case, the separation layer 2having a given pattern is formed by masking etc. or the separation layer2 is formed on the entire surface 11 and is patterned or trimmed byetching etc.

[0161] According to the first and second methods, the transferred layer4 is simultaneously transferred and patterned or trimmed.

[0162] Transfer processes may be repeated two or more times by the sameprocedure. When the transfer processes are performed for an even numbersof times, the positions of the front and rear faces of the transferredlayer formed by the last transfer process are the same as those of thetransferred layer formed on the substrate 1 by the first transferprocess.

[0163] On a large transparent substrate (for example, having aneffective area of 900 mm by 1,600 mm) as a transfer member 6,transferred layers 4 (thin film transistors) formed on small substrates1 (for example, having an effective area of 45 mm by 40 mm) may betransferred side by side by repeating transfer cycles (for example,approximately 800 cycles), so that the transferred layers 4 are formedon the entire effective area of the large transparent substrate. Aliquid crystal display having a size which is the same as that of thelarge transparent substrate can be produced.

[0164] Examples of the first embodiment will now be described.

EXAMPLE 1

[0165] A quartz substrate with a length of 50 mm, a width of 50 mm, anda thickness of 1.1 mm (softening point: 1,630° C., distortion point:1,070° C., and transmittance of excimer laser: approximately 100%) wasprepared, and an amorphous silicon (a-Si) film as a separation layer(laser-absorption layer) was formed on the one side of the quartzsubstrate by a low pressure CVD process (Si₂H₆ gas, 425° C.). Thethickness of the separation layer was 100 nm.

[0166] A SiO₂ film as an interlayer was formed on the separation layerby an ECR-CVD process (SiH₄+O₂ gas, 100° C.). The thickness of theinterlayer was 200 nm.

[0167] A polycrystalline silicon (or polycrystalline silicon) film witha thickness of 50 nm as a transferred layer was formed on the interlayerby a CVD process (Si₂H₆ gas). The polycrystalline silicon film waspatterned to form source/drain/channel regions of a thin filmtransistor. After a SiO₂ gate insulating film was formed by thermaloxidation of the surface of the polycrystalline silicon film, a gateelectrode (a structure in which a high melting point metal, such as Mo,was deposited on the polycrystalline silicon) was formed on the gateinsulating film, and source and drain regions were formed by selfalignment by means of ion implantation using the gate electrode as amask. A thin film transistor was thereby formed.

[0168] A thin film transistor having similar characteristics can beformed by a low temperature process instead of such a high temperatureprocess. For example, an amorphous silicon film with a thickness of 50nm as a transferred layer was formed on a SiO₂ film as an interlayer onthe separation layer by a low pressure CVD process (Si₂H₆ gas, 425° C.),and the amorphous silicon film was irradiated with laser beams(wavelength: 308 nm) to modify the amorphous silicon into apolycrystalline silicon film by crystallization. The polycrystallinesilicon film was patterned to form source/drain/channel regions having agiven pattern of a thin film transistor. After a SiO₂ gate insulatingfilm was deposited on the polycrystalline silicon film by a low pressureCVD process, a gate electrode (a structure in which a high melting pointmetal, such as Mo, was deposited on the polycrystalline silicon) wasformed on the gate insulating film, and source and drain regions wereformed by self alignment by means of ion implantation using the gateelectrode as a mask. A thin film transistor was thereby formed.

[0169] Next, electrodes and leads connected to the source and drainregions and leads connected to the gate electrode were formed, ifnecessary. These electrodes and leads are generally composed ofaluminum, but not for the limitation. A metal (not melted by laserirradiation in the succeeding step) having a melting point higher thanthat of aluminum may be used if melting of aluminum is expected in thesucceeding laser irradiation step.

[0170] A UV-curable adhesive (thickness: 100 μm) was applied onto thethin film transistor, a large, transparent glass substrate (soda glass,softening point: 740° C., distortion point: 511° C.) as a transfermember was adhered to the adhesive film, and the outer surface of theglass substrate was irradiated with ultraviolet rays to fix these layersby curing the adhesive.

[0171] The surface of the quartz substrate was irradiated with Xe—Clexcimer laser beams (wavelength: 308 nm) to cause exfoliations (internaland interfacial exfoliation) of the separation layer. The energy densityof the Xe—Cl excimer laser was 300 mJ/cm², and the irradiation time was20 nano seconds. The excimer laser irradiation methods include aspot-beam irradiation method and a line-beam irradiation method. In thespot-beam irradiation method, a given unit area (for example 8 mm by 8mm) is irradiated with a spot beam, and the spot irradiation is repeatedwhile shifting the spot beam by about one-tenth the given unit area. Inthe line-beam irradiation, a given unit area (for example 378 mm by 0.1mm, or 378 mm by 0.3 mm (absorbing 90% or more of the incident energy))is irradiated while shifting the line-beam by about one-tenth the givenunit area. Each of the points of the separation layer is therebyirradiated at least ten times. The entire surface of the quartzsubstrate is irradiated with the laser, while shifting step by step overthe irradiated area.

[0172] Next, the quartz substrate was detached from the glass substrate(transfer member) at the separation layer, so that the thin filmtransistor and interlayer formed on the quartz substrate weretransferred onto the glass substrate.

[0173] The separation layer remaining on the interlayer on the glasssubstrate was removed by etching, washing, or a combination thereof. Asimilar process was applied to the quartz substrate for recycling thesubstrate.

[0174] When the glass substrate as the transfer member is larger thanthe quartz substrate, the transfer from the quartz substrate to theglass substrate in accordance with this example can be repeated to forma number of thin film transistors on different positions on the quartzsubstrate. A larger number of thin film transistors can be formed on theglass substrate by repeated deposition cycles.

EXAMPLE 2

[0175] A thin film transistor was transferred as in Example 1, but anamorphous silicon film containing 20 atomic percent of hydrogen (H) wasformed as the separation layer. The hydrogen content in the amorphoussilicon film was controlled by the film deposition conditions in the lowpressure CVD.

EXAMPLE 3

[0176] A thin film transistor was transferred as in Example 1, but aceramic thin film (composition: PbTiO₃, thickness: 200 nm) as theseparation layer was formed by spin-coating and sol-gel processes.

EXAMPLE 4

[0177] A thin film transistor was transferred as in Example 1, but aceramic thin film (composition: BaTiO₃, thickness: 400 nm) as theseparation layer was formed by a sputtering process.

EXAMPLE 5

[0178] A thin film transistor was transferred as in Example 1, but aceramic thin film (composition: Pb(Zr,Ti)O₃ (PZT), thickness: 50 nm) asthe separation layer was formed by a laser ablation process.

EXAMPLE 6

[0179] A thin film transistor was transferred as in Example 1, but apolyimide film (thickness: 200 nm) as the separation layer was formed bya spin-coating process.

EXAMPLE 7

[0180] A thin film transistor was transferred as in Example 1, but apolyphenylene sulfide film (thickness: 200 nm) as the separation layerwas formed by a spin-coating process.

EXAMPLE 8

[0181] A thin film transistor was transferred as in Example 1, but analuminum film (thickness: 300 nm) as the separation layer was formed bya sputtering process.

EXAMPLE 9

[0182] A thin film transistor was transferred as in Example 2, but Kr—Fexcimer laser beams (wavelength: 248 nm) were used as the incidentlight. The energy density of the laser beams was 250 mJ/cm², and theirradiation time was 20 nano seconds.

EXAMPLE 10

[0183] A thin film transistor was transferred as in Example 2, butNd-YAG laser beams (wavelength: 1,068 nm) were used as the incidentlight. The energy density of the laser beams was 400 mJ/cm², and theirradiation time was 20 nano seconds.

EXAMPLE 11

[0184] A thin film transistor was transferred as in Example 1, but apolycrystalline silicon film (thickness: 80 nm) as the transferred layerwas formed by a high temperature process at 1,000° C.

EXAMPLE 12

[0185] A thin film transistor was transferred as in Example 1, but atransparent polycarbonate substrate (glass transition point: 130° C.) asthe transfer member was used.

EXAMPLE 13

[0186] A thin film transistor was transferred as in Example 2, but atransparent AS resin substrate (glass transition point: 70 to 90° C.) asthe transfer member was used.

EXAMPLE 14

[0187] A thin film transistor was transferred as in Example 3, but atransparent polymethyl methacrylate substrate (glass transition point:70 to 90° C.) as the transfer member was used.

EXAMPLE 15

[0188] A thin film transistor was transferred as in Example 5, but atransparent polyethylene terephthalate substrate (glass transitionpoint: 67° C.) as the transfer member was used.

EXAMPLE 16

[0189] A thin film transistor was transferred as in Example 6, but atransparent high-density polyethylene substrate (glass transition point:77 to 90° C.) as the transfer member was used.

EXAMPLE 17

[0190] A thin film transistor was transferred as in Example 9, but atransparent polyamide substrate (glass transition point: 145° C.) as thetransfer member was used.

EXAMPLE 18

[0191] A thin film transistor was transferred as in Example 10, but atransparent epoxy resin substrate (glass transition point: 120° C.) asthe transfer member was used.

EXAMPLE 19

[0192] A thin film transistor was transferred as in Example 11, but atransparent polymethyl methacrylate substrate (glass transition point:70 to 90° C.) as the transfer member was used.

[0193] The thin film transistors transferred in Examples 1 to 19 wereobserved visually and with a microscope. All the thin film transistorswere uniformly transferred without forming defects and unevenness.

[0194] As described above, an exfoliating method in accordance with thepresent invention ensures easy and secure exfoliation regardless ofcharacteristics and conditions of the detached member (transferredlayer), and enables transfer onto various transfer members. For example,a thin film can be formed by transfer on a material not capable of ornot suitable for the direct forming of the thin film, an easily formablematerial, an inexpensive material, and a large article which isdifficult to move.

[0195] Materials having thermal and corrosion resistance which isinferior to that of the substrate, for example, various syntheticresins, and low melting point glass materials, can be used as thetransfer member. For example, in the production of a liquid crystaldisplay including thin film transistors (particularly polycrystallinesilicon TFTs) formed on a transparent substrate, a large, inexpensiveliquid crystal display can be easily produced by a combination of aheat-resisting quartz glass substrate as the substrate, and aninexpensive and formable transparent substrate composed of a syntheticresin or a low melting point glass as the transfer member. Such anadvantage will be expected in production of other devices other than theliquid crystal display.

[0196] A transferred layer such as a functional thin film can be formedon a heat-resisting substrate with high reliability, such as a quartzsubstrate, followed by patterning, with maintaining the above-mentionedadvantage. A highly reliable thin film can therefore be formed on atransfer member regardless of the properties of the transfer member.

[0197] [Second Embodiment]

[0198] An exfoliating method in accordance with the second embodiment ofthe present invention will now be described in detail with reference tothe attached drawings. In the second embodiment, the separation layer 2of the first embodiment has a layered structure including a plurality oflayers.

[0199] FIGS. 9 to 16 are cross-sectional views illustrating steps inaccordance with this embodiment in the exfoliating method in accordancewith the present invention. The steps will be described sequentiallywith reference to these drawings. Since many matters are common to thefirst embodiment, the same parts are identified by the same numeral anda detailed description will be omitted appropriately. Accordingly,matters which are different from the first embodiment will be described.

[0200] [1] As shown in FIG. 9, a separation layer 2 composed of acomposite including a plurality of sub-layers is formed on one face (theface 11) of the substrate 1. In this case, each sub-layer in theseparation layer 2 is deposited step by step onto the substrate 1 by amethod described below. Preferably, the substrate 1 is composed of atransparent material transmitting the incident light 7, when the lightis incident on the outer surface of the substrate 1.

[0201] In this case, the transmittance for the incident light 7 issimilar to that in the first embodiment. Materials for the substrate 1are common to the first embodiment. The thickness of the substrate 1 isthe same as that in the first embodiment. It is preferable that thethickness of the substrate 1 be uniform at a region for forming theseparation layer so as to be uniformly irradiated with the incidentlight 7. The inner surface 11 and light-incident surface 12 of thesubstrate 1 may be planar or curved.

[0202] In the present invention, the substrate 1 is detached byexfoliating the separation layer 2 between the substrate 1 and thetransferred layer 4 instead of removing the substrate by etching etc.,hence the operation can be easily performed, and the substrate 1 has awide range of selectivity, for example, use of a relatively thicksubstrate.

[0203] The separation layer 2 is now described. The separation layer 2absorbs the incident light 7 to cause internal and/or interfacialexfoliation of the layer. The separation layer 2 includes at leasttwo-sub layers having different compositions or characteristics, andpreferably an optical absorption layer 21 and other layers having acomposition and characteristics which are different from the opticalabsorption layer 21. It is preferable that the other layer be a shadinglayer (reflection layer 22) for shading the incident light. The shadinglayer lies on the side (upper side in the drawings) of the opticalabsorption layer 21 away from the incident light 7, reflects or absorbsthe incident light 7 to prevent or suppress entry of the incident lightinto the transferred layer 4.

[0204] In this embodiment, a reflection layer 22 reflecting the incidentlight 7 is formed as the shading layer. It is preferable that thereflection layer 22 has a reflectance of 10% or more, and morepreferably 30% or more for the incident light 7. Preferably, such areflection layer 22 is formed of a metallic thin film including asingularity or plurality of sub-layers, or a composite including aplurality of thin films having different refractive indices. Inparticular, it is composed of metallic thin films in view of easyformability.

[0205] Examples of metals suitable for forming a metallic thin filminclude Ta, W, Mo, Cr, Ni, Co, Ti, Pt, Pd, Ag, Au, and Al; and alloysprimarily containing at least one of these metals. Examples ofpreferable elements to be added to such alloys include Fe, Cu, C, Si,and B. The addition of these elements enables control of the thermalconductivity and reflectance of the alloy. Another advantage is easyproduction of a target, when forming the reflection layer by physicaldeposition. Further, alloys can be easily obtained and are inexpensivecompared with the relevant pure metals.

[0206] The thickness of the reflection (shading layer) 22 is preferably10 nm to 10 μm, and more preferably 50 nm to 5 μm, although it is notlimited to such a range. An excessive thickness requires much time forthe formation of the reflection layer 22 and the removal of thereflection layer 22 which will be performed later. A significantly lowthickness may cause insufficient shading effects in some filmcompositions.

[0207] The optical absorption layer 21 contributing to the exfoliationof the separation layer 2 absorbs the incident light 7 to eliminate orreduce inter-atomic or intermolecular adhering forces in the substancesin the optical absorption layer 21 and to cause internal and/orinterfacial exfoliation due to an ablation phenomenon. Further, theirradiation with the incident light 7 may cause exfoliation by theevolution of gas from the optical absorption layer 21. A componentcontained in the optical absorption layer 21 is released as gas in onecase, or the separation layer 2 is instantaneously gasified by absorbingthe light, and the vapor is released to contribute to the exfoliation inthe other case.

[0208] The usable compositions of such an optical absorption layer 21are similar to the compositions (1) to (4) which were described in theseparation layer 2 of the first embodiment. In the second embodiment,the following compositions can also be used as the optical absorptionlayer 21.

[0209] (5) Organic Polymers:

[0210] Usable organic polymers have linkages (which are cut byirradiation of the incident light 7), such as —CH—, —CH₂—, —CO—(ketone), —CONH— (amido), —NH— (imido), —COO—(ester), —N═N— (azo), and—CH═N— (isocyano). In particular, any organic polymers having largeamounts of such linkages can be used. Examples of the organic polymersinclude polyolefins, such as polyethylene, and polypropylene;polyimides; polyamides; polyesters; polymethyl methacrylate (PMMA);polyphenylene sulfide (PPS); polyether sulfone (PES); and epoxy resins.

[0211] (6) Metals:

[0212] Examples of metals include Al, Li, Ti, Mn, In, Sn, and rare earthmetals, e.g. Y, La, Ce, Nd, Pr, Sm, and Gd; and alloys containing atleast one of these metals.

[0213] (7) Hydrogen Occluded Alloys:

[0214] Examples of hydrogen occluded alloys include rare earthelement-based alloys, such as LaNi₅; and Ti- or Ca-based alloys, inwhich hydrogen is occluded.

[0215] (8) Nitrogen Occluded Alloys:

[0216] Examples of nitrogen occluded alloys include rare earthelement-iron, -cobalt, -nickel, and -manganese alloys, such as Sm—Fe andNd—Co alloys, in which nitrogen is occluded.

[0217] The thickness of the optical absorption layer 21 depends onvarious factors, for example, the purpose of the exfoliation, thecomposition of the separation layer 2, the layer configuration, and theformation process, and is generally 1 nm to 20 Am, and preferably 10 nmto 2 μm, and more preferably 40 nm to 1 μm. A significantly lowthickness of the optical absorption layer 21 causes deterioration ofuniformity of the deposited film, and thus irregular exfoliation,whereas an excessive thickness requires a large amount of incident light7 (power) to ensure satisfactory exfoliation and a longer operationaltime for removing the separation layer 2. It is preferable that thethicknesses of the optical absorption layer 21 and reflection layer 22be uniform as much as possible. For the same reasons, the totalthickness of the separation layer 2 is preferably 2 nm to 50 μm, andmore preferably 20 nm to 20 μm.

[0218] The method for forming each layer in the separation layer 2 (inthis embodiment, the optical absorption layer 21 and reflection layer22) is not limited, and is selected in view of various factors, such asthe composition and thickness of the film. Examples of the methodsinclude vapor phase deposition processes, such as CVD (including MOCVD,low pressure CVD, ECR-CVD), evaporation, molecular beam (MB)evaporation, sputtering, ion-plating, and PVD; plating processes, suchas electroplating, dip-plating (dipping), and electroless-plating;coating process, such as a Langmuir-Blodgett process, spin-coatingprocess, spray-coating process, and roll-coating process; printingprocesses; transfer processes; ink-jet processes; and powder-jetprocesses. A combination of these processes may also be usable. Theprocess for forming the optical absorption layer 21 and reflection layer22 may be the same or different, and is determined by the compositionetc.

[0219] For example, when the optical absorption layer 21 is composed ofamorphous silicon (a-Si), it is preferable that the layer be formed by alow pressure CVD process or a plasma CVD process. Alternatively, whenthe optical absorption layer 21 is composed of a ceramic by a sol-gelprocess, or an organic polymer, it is preferable that the layer beformed by a coating process, and particularly a spin-coating process.

[0220] The reflection layer 22 composed of a metallic thin film ispreferably formed by evaporation, molecular beam (MB) evaporation, laserablation deposition, sputtering, ion plating, and the above-mentionedplating processes.

[0221] Each layer in the separation layer 2 may be formed by two or moresteps, for example, including a layer forming step and an annealingstep.

[0222] [2] As shown in FIG. 10, an interlayer (underlying layer) 3 isformed on the separation layer 2.

[0223] The interlayer 3 is formed for various purposes, and functions asat least one layer of, for example, a protective layer which protectsphysically or chemically a transferred layer 4 in production and in use,an insulating layer, a conductive layer, a shading layer of the incidentlight 7, a barrier layer inhibiting migration of any components from orto the transferred layer 4, and a reflection layer.

[0224] The composition of the interlayer 3 is determined based on thepurpose: For example, the interlayer 3, which is formed between theseparation layer 2 with the amorphous silicon optical absorption layer21 and the transferred layer 4 as the thin film transistor, is composedof silicon oxide, e.g. SiO₂, or the interlayer 3 formed between theseparation layer 2 and the PZT transferred layer 4 is composed of ametal, e.g. Pt, Au, W, Ta, Mo, Al, Cr, or Ti, or an alloy primarilycontaining such a metal.

[0225] The thickness of the interlayer 3 is similar to that in the firstembodiment. The method for forming the interlayer 3 is also similar tothat in the first embodiment. The interlayer 3 may be composed of two ormore layers having the same composition or different compositions.Alternatively, in the present invention, the transferred layer 4 may bedirectly formed on the separation layer 2 without forming the interlayer3.

[0226] [3] As shown in FIG. 11, a transferred layer (detached member) 4is formed on the interlayer 3. The transferred layer 4 is transferredonto a transfer member 6 which will be described later, and formed by amethod similar to that for the separation layer 2. The purpose forforming, type, shape, structure, composition, and physical and chemicalcharacteristics of the transferred layer 4 are not limited, and it ispreferable that the transferred layer 4 be a functional thin film or athin film device in view of the purpose and usefulness of the transfer.Examples of the functional thin films and thin film devices have beendescribed in the first embodiment.

[0227] Such a functional thin film or thin film device is generallyformed at a relatively high process temperature in connection with themanufacturing method. As described above, therefore, the substrate 1must be highly reliable and resistive to such a high processtemperature.

[0228] The transferred layer 4 may be composed of a single layer or aplurality of layers. Additionally, it may be patterned as in theabove-described thin film transistor. The formation (deposition) andpatterning of the transferred layer 4 is performed by a given processaccording to demand. Such a transferred layer 4 is generally formed by aplurality of steps. The thickness of the transferred layer 4 is alsosimilar to that in the first embodiment.

[0229] [4] As shown in FIG. 12, an adhesive layer 5 is formed on thetransferred layer (exfoliation layer) 4 to adhere with the transfermember 6 through the adhesive layer 5. Preferred examples of adhesivesfor forming the adhesive layer 5 are identical to those in the firstembodiment. When using a curable adhesive, the curable adhesive isapplied onto the transferred layer 4, a transfer member 6 describedlater is adhered thereto, the curable adhesive is cured by a curingmethod in response to the property to adhere the transferred layer 4with the transfer member 6. In the case using a photo-setting adhesive,it is preferable that a transparent transfer member 6 be placed on theadhesive layer 5, and then the transfer member 6 be irradiated withlight to cure the adhesive. When the substrate 1 is transparent, boththe substrate 1 and the transfer member 6 are preferably irradiated withlight to secure curing of the adhesive.

[0230] Instead of the state shown in the drawings, the adhesive layer 5may be formed on the side of the transfer member 6, and the transferredlayer 4 may be formed thereon. Further, the above-mentioned interlayermay be formed between the transferred layer 4 and the adhesive layer 5.When, for example, the transfer member 6 has a function as an adhesive,the formation of the adhesive layer 5 can be omitted.

[0231] Examples, materials, and characteristics of the transfer member 6are identical to those in the first embodiment.

[0232] [5] As shown in FIG. 13, the rear side (the incident face 12) ofthe substrate 1 is irradiated with the incident light 7. After theincident light 7 passes through the substrate 1, it is radiated to theseparation layer 2 through the interface 2 a. In detail, it is absorbedin the optical absorption layer 21, the part of the incident light 7 notabsorbed in the optical absorption layer 21 is reflected by thereflection layer 22 and passes through the optical absorption layer 21again. The adhering force in the separation layer is reduced oreliminated by the internal and/or interfacial exfoliation, and as shownin FIG. 14 or 15, the transferred layer 4 is detached from the substrateand transferred onto the transfer member 6 when the substrate 1 isseparated from the transfer member 6.

[0233]FIG. 14 shows a case of internal exfoliation of the separationlayer 2, and FIG. 15 shows a case of interfacial exfoliation at theinterface 2 a of the separation layer 2. It is presumed from theoccurrence of an internal and/or interfacial exfoliation that ablationof the constituents in the optical absorption layer 21 occurs, that gasretained in the optical absorption layer 21 is released, and that phasechange such as melting or vaporization occurs immediately after theirradiation of the light.

[0234] Wherein the word “ablation” means that solid components (theconstituents of the optical absorption layer 21), which absorbed theincident light, are photochemically and thermally excited and atoms andmolecules in the solid components are released by the chain scission.The ablation is observed as phase transition such as melting orvaporization in the partial or entire constituents of the opticalabsorption layer 21. Also, fine foaming may be formed by the phasechange, resulting in a reduced adhering force. The internal and/orinterfacial exfoliation of the separation layer 21 depends on the layerconfiguration of the separation layer 2, the composition and thicknessof the optical absorption layer 21 and other factors, for example, thetype, wavelength, intensity and, range of the incident light 7.

[0235] Examples of types of the incident light 7 and of apparatuses forgenerating it are identical to those in the first embodiment.

[0236] When the ablation in the optical absorption layer 21 depends onthe wavelength of the incident light, it is preferable that thewavelength of the incident laser light ranges from approximately 100 nmto 350 nm. When exfoliating the separation layer 2 by the phasetransition such as gas evolution, vaporization, and sublimation, thewavelength of the incident laser light preferably ranges fromapproximately 350 nm to 1,200 nm. The energy density of the incidentlaser light, and particularly of the excimer laser light preferablyranges from approximately 10 to 5,000 mJ/cm², and more preferably from100 to 1,000 mJ/cm². The preferable irradiation time ranges from 1 to1,000 nano seconds, and more preferably 10 to 100 nano seconds. A lowerenergy density or a shorter irradiation time may cause insufficientablation, whereas a higher energy density or a longer irradiation timemay cause excessive breakage of the separation layer 2. It is preferablethat the incident light 7 such as laser light be incident such that theintensity is uniform.

[0237] The direction of the incident light 7 is not limited to thedirection perpendicular to the separation layer 2, and may be shifted byseveral degrees from the perpendicular direction if the area of theseparation layer 2 is larger than the irradiation area per scan of theincident light, the entire region of the separation layer 2 may beirradiated two or more times at the same position. Alternatively, thesame position or different positions may be irradiated with differenttypes or different wavelengths (wavelength regions) of the incidentlight (laser light).

[0238] In this embodiment, the reflection layer 22 is provided at theside of the optical absorption layer 21 away from the substrate 1, hencethe optical absorption layer 21 can be effectively irradiated with theincident light 7 without any loss. Further, the irradiation of thetransferred layer 4 with the incident light 7 can be prevented by theshading characteristics of the reflection layer (shading layer),preventing adverse effects, such as the modification and deteriorationof the transferred layer 4.

[0239] In particular; since the optical absorption layer 21 isirradiated with the incident light without loss, the energy density ofthe incident light 7 can be reduced, or in other words, the irradiationarea per scan can be increased; a given area of the separation layer 2can therefore be exfoliated at decreased irradiation times as anadvantage in the production process.

[0240] [6] As shown in FIG. 16, the separation layer 2 remaining on theinterlayer 3 is removed by, for example, washing, etching, ashing, orpolishing, or a combination thereof. In the internal exfoliation of theseparation layer 2 shown in FIG. 14, the optical absorption layer 21remaining on the substrate 1 can also be removed if necessary.

[0241] When the substrate 1 is composed of an expensive or rare materialsuch as quartz glass, it is preferable that the substrate 1 be reused(recycled). In other words, the present invention is applicable to asubstrate to be reused, and thus is highly useful.

[0242] The transfer of the transferred layer 4 onto the transfer member6 is completed by these steps. The removal of the interlayer 3 adjoiningthe transferred layer 4 and formation of an additional layer may beincorporated.

[0243] The configuration of the separation layer 2 is not limited tothat shown in the drawings, and may include that comprising a pluralityof optical absorption layers which have at least one different propertyamong the composition, thickness, and characteristics of the layer. Forexample, the separation layer 2 may be composed of three layersincluding a first optical absorption layer, a second optical absorptionlayer, and a reflection layer provided therebetween.

[0244] The interfaces between the sub-layers forming the separationlayer 2 are not always clearly provided, the composition of the layer,and the concentration, molecular structure, and physical and chemicalproperties of a given component may continuously change (may have agradient) near the interface.

[0245] In this embodiment shown in the drawings, the transfer of thetransferred layer 4 onto the transfer member 6 is described, suchtransfer is not always incorporated in the exfoliating method inaccordance with the present invention.

[0246] The exfoliating member can be used for various purposes asdescribed in the first embodiment. Various transfer members 6 other thanthat described above can also be used as in the first embodiment.

[0247] When the adhered member (detached member) is removed or when thetransferred layer 4 is not adversely affected by the incident light 7,the incident light 7 is not always incident on the substrate 1, and maybe incident on the side away from the substrate 1. In this case, it ispreferable that the optical absorption layer 21 and the reflection layer22 have a reversed positional relationship in the separation layer 2.

[0248] The exfoliating method in accordance with the present inventionhas been described with reference to this embodiment shown in thedrawings, the present invention, however, is not limited to this, andpermits various modifications as in the first embodiment (please referto the description concerning the modifications in the firstembodiment).

[0249] Examples of the second embodiment will now be described.

EXAMPLE 1

[0250] A quartz substrate with a length of 50 mm, a width of 50 mm, anda thickness of 1.1 mm (softening point: 1,630° C., distortion point:1,070° C., and transmittance of excimer laser: approximately 100%) wasprepared, and a separation layer having a double-layered structureincluding an optical absorption layer and a reflecting layer was formedon one side of the quartz substrate.

[0251] An amorphous silicon (a-Si) film as the optical absorption layerwas formed by a low pressure CVD process (Si₂H₆ gas, 425° C.). Thethickness of the optical absorption layer was 100 nm. A metallic thinfilm composed of Ta as the reflecting layer was formed on the opticalabsorption layer by a sputtering process. The thickness of thereflection layer was 100 nm, and the reflectance of the laser light was60%.

[0252] A SiO₂ film as an interlayer was formed on the separation layerby an ECR-CVD process (SiH₄+O₂ gas, 100° C.). The thickness of theinterlayer was 200 nm.

[0253] An amorphous silicon film with a thickness of 60 nm as atransferred layer was formed on the interlayer by a low pressure CVDprocess (Si₂H₆ gas, 425° C.), and the amorphous silicon film wasirradiated with laser light beams (wavelength: 308 nm) to modify theamorphous silicon film into a polycrystalline silicon film bycrystallization. The polycrystalline silicon film was subjected topatterning and ion plating to form a thin film transistor.

[0254] A UV-curable adhesive (thickness: 100 μm) was applied onto thethin film transistor, a large, transparent glass substrate (soda glass,softening point: 740° C., distortion point: 511° C.) as a transfermember was adhered to the adhesive film, and the outer surface of theglass substrate was irradiated with ultraviolet rays to fix these layersby curing the adhesive.

[0255] The surface of the quartz substrate was irradiated with Xe—Clexcimer laser beams (wavelength: 308 nm) to cause exfoliation (internaland interfacial exfoliation) of the separation layer. The energy densityof the Xe—Cl excimer laser was 160 mJ/cm², and the irradiation time was20 nano seconds. The excimer laser irradiation methods include aspot-beam irradiation method and a line-beam irradiation method. In thespot-beam irradiation method, a given unit area (for example 10 mm by 10mm) is irradiated with a spot beam, and the spot irradiation is repeatedwhile shifting the spot beam by about one-tenth the given unit area. Inthe line-beam irradiation, a given unit area (for example 378 mm by 0.1mm, or 378 mm by 0.3 mm (absorbing 90% or more of the incident energy))is irradiated with while shifting the line-beam by about one-tenth thegiven unit area. Each of the points of the separation layer is therebyirradiated at least ten times. The entire surface of the quartzsubstrate is irradiated with the laser, while shifting step by step theirradiated area.

[0256] Next, the quartz substrate was detached from the glass substrate(transfer member) at the separation layer, so that the thin filmtransistor and interlayer were transferred onto the glass substrate.

[0257] The separation layer remaining on the interlayer on the glasssubstrate was removed by etching, washing, or a combination thereof. Asimilar process was applied to the quartz substrate for recycling thesubstrate.

EXAMPLE 2

[0258] A thin film transistor was transferred as in Example 1, but anamorphous silicon film containing 18 atomic percent of hydrogen (H) wasformed as the optical absorption layer. The hydrogen content in theamorphous silicon film was controlled by the film deposition conditionsin the low pressure CVD.

EXAMPLE 3

[0259] A thin film transistor was transferred as in Example 1, but aceramic thin film (composition: PbTiO₃, thickness: 200 nm) as theoptical absorption layer was formed by spin-coating and sol-gelprocesses.

EXAMPLE 4

[0260] A thin film transistor was transferred as in Example 1, but aceramic thin film (composition: BaTiO₃, thickness: 400 nm) as theoptical absorption layer, and a metallic thin film composed of aluminum(thickness: 120 nm, reflectance of laser light: 85%) as the reflectionlayer were formed by a sputtering process.

EXAMPLE 5

[0261] A thin film transistor was transferred as in Example 1, but aceramic thin film (composition: Pb(Zr,Ti)O₃ (PZT), thickness: 50 nm) asthe optical absorption layer was formed by a laser ablation process, anda metallic thin film (thickness: 80 nm, reflectance of laser light: 65%)composed of an Fe—Cr alloy was formed by a sputtering process.

EXAMPLE 6

[0262] A thin film transistor was transferred as in Example 1, but apolyimide film (thickness: 200 nm) as the optical absorption layer wasformed by a spin-coating process.

EXAMPLE 7

[0263] A thin film transistor was transferred as in Example 1, but apraseodymium (Pr) film (rare earth metal film) (thickness: 500 nm) asthe optical absorption layer was formed by a sputtering process.

EXAMPLE 8

[0264] A thin film transistor was transferred as in Example 2, but Kr—Fexcimer laser beams (wavelength: 248 nm) were used as the incidentlight. The energy density of the laser beams was 180 mJ/cm², and theirradiation time was 20 nano seconds.

EXAMPLE 9

[0265] A thin film transistor was transferred as in Example 2, but Arlaser beams (wavelength: 1,024 nm) were used as the incident light. Theenergy density of the laser beams was 250 mJ/cm², and the irradiationtime was 50 nano seconds.

EXAMPLE 10

[0266] A thin film transistor was transferred as in Example 1, but apolycrystalline silicon film (thickness: 90 nm) as the transferred layerwas formed by a high temperature process at 1,000° C.

EXAMPLE 11

[0267] A thin film transistor was transferred as in Example 2, but apolycrystalline silicon film (thickness: 80 nm) as the transferred layerwas formed by a high temperature process at 1,030° C.

EXAMPLE 12

[0268] A thin film transistor was transferred as in Example 4, but apolycrystalline silicon film (thickness: 80 nm) as the transferred layerwas formed by a high temperature process at 1,030° C.

EXAMPLES 13 to 20

[0269] A series of thin film transistors were transferred as in Examples12 to 19 of the first embodiment.

[0270] The thin film transistors transferred in Examples 1 to 20 wereobserved visually and with a microscope. All the thin film transistorswere uniformly transferred without forming defects and unevenness.

[0271] As described above, the second embodiment in accordance with thepresent invention has advantages shown in the first embodiment, thetransferred layer, such as a thin film transistor, is prevented fromadverse affects by the transmission of the incident light when theseparation layer includes a shading layer, and particularly a reflectionlayer, and the separation layer is more effectively exfoliated by theuse of the reflecting light from the reflection layer.

[0272] [Third Embodiment]

[0273] An exfoliating method in accordance with the third embodiment ofthe present invention will now be described in detail with reference tothe attached drawings. In the third embodiment, a thin film device isused as the detached member or the transferred layer in the firstembodiment.

[0274] FIGS. 17 to 22 are cross-sectional views illustrating steps inaccordance with this embodiment in the exfoliating method in accordancewith the present invention. Each of the steps of the exfoliating method(transferring method) will be described with reference to thesedrawings. Since many matters are common to the first embodiment, thesame parts are identified by the same numerals and a detaileddescription will be omitted appropriately. Accordingly, matters whichare different from the first embodiment will be described.

[0275] [Step 1] As shown in FIG. 17, a separation layer (opticalabsorption layer) is formed on a substrate 100. The substrate 100 andthe separation layer 120 will be described.

[0276] (1) Description of the Substrate 100

[0277] Preferably, the substrate 100 is composed of a transparentmaterial which transmits light. The light transmittance is identical tothe first embodiment. Also, the material and the thickness of thesubstrate 100 are identical to the first embodiment.

[0278] (2) Description of the Separation Layer 120

[0279] The separation layer 120 absorbs the incident light to causeinternal and/or interfacial exfoliation, and preferably is composed of amaterial in which inter-atomic or inter-molecular adhering forces arereduced or eliminated by light irradiation to cause internal and/orinterfacial exfoliation based on ablation.

[0280] Further, gas causing exfoliating effects may be released from theseparation layer 120 by light irradiation in some cases, that is, a casein which components contained in the separation layer 120 are releasedas gas, and a case in which the separation layer 120 is instantaneouslygasified by absorbing the incident light and the released vaporcontributes to exfoliation. The composition of such a separation layer120 is similar to that in the first embodiment.

[0281] Also, the thickness of the separation layer 120 and the methodfor forming it are similar to those in the first embodiment.

[0282] [Step 2] Next, as shown in FIG. 18, a transferred layer (thinfilm device layer) 140 is formed on the separation layer 120. Anenlarged cross-sectional view of the portion K (surrounded by a dottedline in FIG. 18) of the thin film device layer 140 is shown in the rightside of FIG. 18. As shown in the drawing, the thin film device layer 140is composed of a TFT (thin film transistor) formed on a SiO₂ film(interlayer) 142, and the TFT includes source and drain layers 146composed of an n-doped polycrystalline silicon layer, a channel layer144, a gate insulating film 148, a gate electrode 150, an insulatinginterlayer 154, and an electrode composed of, for example, aluminum.

[0283] In this embodiment, although the interlayer adjoining theseparation layer 120 is composed of a SiO₂ film, it may be composed ofany other insulating film, such as Si₃N₄. The thickness of the SiO₂ film(interlayer) is adequately determined based on the purpose for theformation and its functions, and ranges generally from approximately 10nm to 5 μm, and preferably 40 nm to 1 μm. The interlayer is formed forvarious purposes, and functions as at least one of a protective layerphysically or chemically protecting the transferred layer 140, aninsulating layer, a conductive layer, a shading layer to laser light, abarrier layer for preventing migration, and a reflection layer.

[0284] In some cases, the transferred layer (thin film device layer) 140may be directly formed on the separation layer 120, by omitting theformation of the interlayer, such as the SiO₂ film.

[0285] The transferred layer (thin film device layer) 140 includes athin film device such as a TFT, as shown in the right side of FIG. 18.As well as a TFT, other thin film devices shown in the first embodimentcan also be used. These thin film devices are generally formed at arelatively high process temperature inherent to the formation method.Thus, as described above, the substrate 100 must have high reliabilityand must be resistant to the process temperature.

[0286] [Step 3] As shown in FIG. 19, the thin film device layer 140 isadhered to a transfer member 180 using an adhesive layer 160. Preferableexamples of adhesives forming the adhesive layer 160 are described inthe first embodiment.

[0287] When using a curable adhesive, for example, the curable adhesiveis applied onto the transferred layer (thin film device layer) 140, thetransfer member 180 is adhered thereto, the curable adhesive is cured bya curing method in response to the property to adhere the transferredlayer (thin film device layer) 140 with the transfer member 180. In thecase where a photo-setting adhesive is used, the outer surface of thetransparent substrate 100 or transparent transfer member 180 (or bothouter surfaces of the transparent substrate and transparent transfermember) is irradiated with light. A photo-setting adhesive, which barelyaffects the thin film device layer, is preferably used as the adhesive.

[0288] Instead of the method shown in the drawing, the adhesive layer160 may be formed on the transfer member 180 and the transferred layer(thin film device layer) 140 may be adhered thereto. Alternatively, theformation of the adhesive layer 160 can be omitted when the transfermember 180 has adhesive characteristics.

[0289] Examples of the transfer members 180 are described in the firstembodiment.

[0290] [Step 4] As shown in FIG. 20, the rear side of the substrate 100is irradiated with light. The light passing through the substrate 100 isincident on the separation layer 120. As a result, internal and/orinterfacial exfoliation, which reduces or eliminates the adheringforces, occurs. It is presumed from the occurrence of the internaland/or interfacial exfoliation in the separation layer 120 that ablationof the constituents in the separation layer 120 occurs, that gasretained in the separation layer 120 is released, and that phasetransition such as melting or vaporization occurs immediately after thelight irradiation.

[0291] The word “ablation” has the same meaning as in the firstembodiment.

[0292] The incident light is identical to the light used in the firstembodiment. In particular, excimer lasers are preferably used. Theexcimer lasers output high energy laser beams in a shorter wavelengthrange which cause ablation in the separation layer 120 within asignificantly shorter time. The separation layer 120 is thereforecleaved substantially without the temperature rise, and thus withoutdeterioration or damage of the adjacent or adjoining transfer member180, and substrate 100.

[0293] If the ablation of the separation layer 120 is dependent on thewavelength of the incident light, it is preferable that the wavelengthof the incident laser beam be approximately 100 nm to 350 nm.

[0294]FIG. 23 is a graph of transmittance vs. wavelength of light in thesubstrate 100. As shown in the graph, the transmittance increasessteeply at a wavelength of 300 nm. In such a case, light beams having awavelength of higher than 300 nm (for example, Xe—Cl excimer laser beamshaving a wavelength of 308 nm) are used. When exfoliating the separationlayer 120 by means of phase transition, for example, gas evolution,vaporization, or sublimation, it is preferable that the wavelength ofthe incident laser beam be approximately 350 nm to 1,200 nm.

[0295] The energy density of the incident laser light beam, andparticularly of the excimer laser light beam, is similar to that in thefirst embodiment.

[0296] When the light passing through the separation layer 120 reachesthe transferred layer 140 and adversely affects the layer, a metallicfilm 124 composed of tantalum (Ta) etc. may be formed on the separationlayer (laser absorption layer) 120. The laser light passing through theseparation layer 120 is completely reflected on the interface with themetallic film 124, and thus does not affect the thin film deviceprovided on the metallic film. It is preferable that the intensity ofthe incident light such as laser light be uniform. The direction of theincident light is not always perpendicular to the separation layer 120,and may be shifted by a given angle from the perpendicular direction.

[0297] If the area of the separation layer 120 is larger than theirradiation area per scan of the incident light, the entire region ofthe separation layer 120 may be irradiated two or more times at the sameposition. Alternatively, the same position or different positions may beirradiated with different types or different wavelengths (wavelengthregions) of the incident light (laser light).

[0298] Next, as shown in FIG. 21, the substrate 100 is detached from theseparation layer 120 by applying a force to the substrate 100. A part ofthe separation layer may remain on the substrate after the detachment,not shown in FIG. 21.

[0299] As shown in FIG. 22, the residual separation layer 120 is removedby etching, ashing, washing, polishing or a combination thereof. Thetransferred layer (thin film device layer) 140 is thereby transferredonto the transfer member 180. Also, the moiety of the separation layerremaining on the substrate 100 is removed. When the substrate 100 iscomposed of an expensive or rare material such as quartz glass, it ispreferably reused (recycled). That is, the present invention isapplicable to the substrate 100 to be reused, and is useful.

[0300] The transfer of the transferred layer (thin film device layer)140 onto the transfer member 180 is completed by these steps. The SiO₂film adjoining the transferred layer (thin film device layer) 140 may beremoved, or a conductive layer for wiring and/or a protective film maybe formed on the transferred layer 140.

[0301] In the present invention, the transferred layer (thin film devicelayer) 140 is not directly separated as the detached member, but theseparation layer adhered to the transferred layer (thin film devicelayer) 140 is exfoliated, hence uniform exfoliation or transfer iseasily, securely, and uniformly achieved regardless of characteristicsand conditions of the detached member (transferred layer 140). Since thedetached member (transferred layer 140) is not damaged during theexfoliating operation, it can maintain high reliability.

[0302] Examples 1 to 19 in the first embodiment can also be applied tothe third embodiment.

[0303] [Fourth Embodiment]

[0304] The fourth embodiment includes a modification of a step in thethird embodiment.

[0305] [Formation of an Amorphous Silicon Layer in the Step 1]

[0306] When the separation layer 120 is composed of amorphous silicon(a-Si), it is preferably formed by a chemical vapor deposition (CVD)process, and particularly by a low pressure (LP) CVD process, comparedwith plasma CVD, atmospheric pressure (AP) CVD, and ECR processes. Forexample, an amorphous silicon layer formed by the plasma CVD processcontains a relatively large quantity of hydrogen. The presence ofhydrogen makes the ablation of the amorphous silicon layer easy, whereinhydrogen is released from the amorphous silicon layer at a temperatureof higher than 350° C. The evolution of hydrogen during the step formingthe thin film device may cause exfoliation of the film. Further, theplasma CVD film has relatively low adhesiveness, hence the substrate 100may be detached from the transferred layer 140 in the wet washing stepin the production of the device. In contrast, the LPCVD film has nopossibility of evolution of hydrogen and has sufficient adhesiveness.

[0307] The thickness of the amorphous silicon layer 120 as theseparation layer will be described with reference to FIG. 39. In FIG.39, the horizontal axis represents the thickness of the amorphoussilicon layer, and the vertical axis represents the optical energyabsorbed in this layer. As described above, when the amorphous siliconlayer is irradiated with light, ablation occurs.

[0308] The word “ablation” means that solid components (the constituentsof the separation layer 120), which absorbed the incident light, arephotochemically and thermally excited and atoms and molecules in thesolid components are released by the chain scission. The ablation isobserved as phase transition such as melting or vaporization in thepartial or entire constituents of the separation layer 120. Also, finefoaming may be formed by the phase change, resulting in a decreasedadhering force.

[0309] The absorbed energy required for the ablation decreases with adecreased thickness, as shown in FIG. 39.

[0310] Accordingly, the thickness of the amorphous silicon layer 120 asthe separation layer is reduced in this embodiment. The energy of thelight incident on the amorphous silicon layer 120 is thereby reduced,resulting in lower energy consumption and miniaturization of the lightsource unit.

[0311] The thickness level of the amorphous silicon layer 120 as theseparation layer will now be investigated. As shown in FIG. 39, theabsorbed energy required for the ablation decreases as the thickness ofamorphous silicon decreases. According to the present inventorsinvestigation, it is preferable that the thickness be 25 nm or less,hence ablation can occur by the power of a general light source unit.Although the lower limit of the thickness is not limited, a lower limitof 5 nm may be determined in view of the secure formation andadhesiveness of the amorphous silicon layer. Accordingly, the preferablethickness of the amorphous silicon layer 120 ranges from 5 nm to 25 nm,and more preferably 15 nm or less for achieving further energy savingand higher adhesiveness. The optimum range of the thickness is 11 nm orless, and the absorbed energy required for the ablation can besignificantly decreased near the thickness.

[0312] [Fifth Embodiment]

[0313] The fifth embodiment includes a modification of a step in thethird or fourth embodiment.

[0314] [Reinforcement of the Transfer Member in the Step 3]

[0315] Although the transfer member 180 has preferably a certain amountof rigidity as a mechanical property, it may have flexibility orelasticity. Such a mechanical property of the transfer member 180 isdetermined in consideration of the following point. When the separationlayer 120 is irradiated with light, the constituent material of theseparation layer 120 is photochemically or thermally excited, andmolecules or atoms on and in the layer are cleaved to release moleculesor atoms outside. It is preferable that the transfer member 180 hasmechanical strength which is resistant to the stress acting on the upperportion of the separation layer 120 accompanied by the release ofmolecules or atoms. A deformation or breakage at the upper portion ofthe separation layer 120 can be thereby prevented.

[0316] Such mechanical strength may be imparted not only to the transfermember 180, but also to at least one layer lying above the separationlayer 120, that is, the transferred layer 140, the adhesive layer 160,and the transfer member 180. The materials for and thicknesses of thetransferred layer 140, adhesive layer 160, and transfer member 180 canbe determined in order to achieve such mechanical strength.

[0317] When a combination of the transferred layer 140, adhesive layer160 and transfer member 180 does not have sufficient mechanicalstrength, a reinforcing layer 132 may be formed at an appropriateposition above the separation layer 120, as shown in FIGS. 42(A) to42(E).

[0318] The reinforcing layer 132 shown in FIG. 42(A) is provided betweenthe separation layer 120 and the transferred layer 140. After formingexfoliation in the separation layer 120 and detaching the substrate 100,the reinforcing layer 132 can be removed together with the remainingseparation layer 120 from the transferred layer 140. As shown in FIG.42(B), the reinforcing layer 132 provided above the transferred layer180 can also be removed from the transferred layer 180, after theseparation layer 120 is cleaved. The reinforcing layer 132 shown in FIG.42(C) intervenes as, for example, an insulating layer in the transferredlayer 140 composed of a plurality of layers. Each reinforcing layer 132shown in FIGS. 42(D) and 42(E) is placed under or on the adhesive layer160. In such a case, it cannot be removed later.

[0319] [Sixth Embodiment]

[0320] The sixth embodiment includes a modification of a step in any oneof the third, fourth, and fifth embodiments.

[0321] [Formation of an Amorphous Silicon-Based Optical Absorption Layeras the Separation Layer in the Step 4]

[0322] It is preferable that a method shown in FIG. 40 or 41 be employedinstead of the method shown in FIG. 38. In FIG. 40, an amorphous siliconlayer 120 is employed as the separation layer, and another amorphoussilicon layer 126 is also employed as a silicon-based optical absorptionlayer. In order to separate these two amorphous silicon layers 120 and126, a silicon oxide (SiO₂) film intervenes as a silicon-basedintervening layer. Even if the-incident light passes through theamorphous silicon layer 120 as the separation layer, the transmittedlight is absorbed in the amorphous silicon layer 126 as thesilicon-based optical absorption layer. As a result, the thin filmdevice provided thereon is not adversely affected. Since the twoadditional layers 126 and 128 are composed of silicon, metalliccontamination etc. does not occur in an established conventional filmdeposition technology.

[0323] When the thickness of the amorphous silicon layer 120 as theseparation layer is larger than the thickness of the amorphous siliconlayer 126 as the optical absorption layer, exfoliation in the amorphoussilicon layer 126 can be securely prevented. Regardless of such arelationship of the thicknesses, however, the optical energy incident onthe amorphous silicon layer 126 is considerably lower than the opticalenergy incident on the amorphous silicon layer 120 as the separationlayer, no ablation occurs in the amorphous silicon layer 126.

[0324]FIG. 41 shows a case providing a silicon-based optical absorptionlayer 130 composed of a different material from that of the separationlayer 120, wherein the silicon-based intervening layer is not alwaysnecessary.

[0325] When a countermeasure to optical leakage in the separation layer120 is employed as shown in FIG. 40 or 41, adverse effects to the thinfilm device can be securely prevented even if the optical absorptionenergy for exfoliating the separation layer 120 is high.

[0326] [Seventh Embodiment]

[0327] The seventh embodiment includes a modification of a step in anyone of the third to sixth embodiments.

[0328] [Modification of Irradiation with Light in the Step 4]

[0329] A method of irradiation with light, which is suitable for a casenot having a metallic film 124 shown in FIG. 38 and does not affect thethin film device, will now be described with reference to the drawingsfrom FIG. 43 onwards.

[0330]FIGS. 43 and 44 show a method for irradiating almost the entireseparation layer 120 with light. In each drawing, the number of scanningtimes of line beams is represented by N, and beam scanning is performedsuch that the region 20(N) irradiated with the N-th line beam 10 doesnot overlap with the region 20(N+1) irradiated with the (N+1)-th linebeam 10. As a result, a low- or non-irradiation region 30 which issignificantly narrower than each irradiated region is formed between thetwo adjacent regions 20(N) and 20(N+1).

[0331] When the line beam 10 is moved to the direction shown by thearrow A in relation to the substrate 100 while radiating the beam, alow-irradiation region 30 is formed. Alternatively, when the beam is notradiated during such a movement, a non-irradiation region 30 is formed.

[0332] If the regions irradiated by different line beams overlap witheach other, the separation layer 120 is irradiated with an excessiveamount of incident light which is larger than that required for internaland/or interfacial exfoliation. When the light leaked from theseparation layer 120 is incident on the transferred layer 140 includinga thin film device, electrical and other characteristics of the thinfilm device will deteriorate.

[0333] In the method shown in FIGS. 43 and 44, the separation layer 120is not irradiated with such excessive light, hence the originalcharacteristics inherent to the thin film device can be maintained afterthe it is transferred onto the transfer member. Although exfoliatingdoes not occur in the low- or non-irradiation region 30 in theseparation layer 120, the adhesiveness between the separation layer 120and the substrate 100 can be satisfactorily reduced by exfoliating inthe regions irradiated with the line beams.

[0334] An example of beam scanning in view of the intensity of the linebeam 10 will be described with reference to FIGS. 44 to 47.

[0335] In FIG. 44, beam scanning is performed such that the region 20(N)irradiated with the N-th line beam 10 overlaps with the region 20(N+1)irradiated with the (N+1)-th line beam 10. A doubly-irradiated region 40is therefore formed between the two adjacent regions 20(N) and 20(N+1).

[0336] The following description is an explanation of why leakage causedby excessive incident light does not occur in the doubly-irradiatedregion 40 in the separation layer 120 and why the originalcharacteristics of the thin film device can be maintained.

[0337]FIGS. 46 and 47 are graphs of distributions of optical intensityvs. the position of the two adjacent line beams 10 and 10 in beamscanning.

[0338] In accordance with the distribution of the optical intensityshown in FIG. 46, each line beam 10 has a flat peak 10 a having amaximum intensity at a predetermined region including the beam center.The two adjacent line beams 10 and 10 are scanned such that the twocorresponding flat peaks 10 a do not overlap with each other.

[0339] In contrast, according to the distribution of the opticalintensity shown in FIG. 47, each line beam 10 has a beam center with amaximum intensity, wherein the optical intensity decreases at a pointdistant from the beam center. The two adjacent line beams 10 and 10 arescanned such that the two beam-effective regions having an intensitywhich is 90% of the maximum intensity of each line beam 10 do notoverlap with each other.

[0340] As a result, the total dose (summation of products of opticalintensities by irradiated times at each position) of the light beamsincident on the doubly-irradiated region 40 is lower than that of theflat region or beam-effective region. The doubly-irradiated region 40,therefore, will first be cleaved at the second irradiation of the beams,and this does not correspond to the excessive irradiation of beam. Ifthe relevant region of the separation layer is cleaved at the firstirradiation, the intensity in the second irradiation of the light beam,which is incident on the thin film device, is reduced, hencedeterioration of the electrical characteristics of the thin film devicecan be prevented or significantly reduced to a practical level.

[0341] In order to suppress leakage of light in the doubly-irradiatedregion 40, it is preferable that the intensity of each beam which isincident on the doubly-irradiated region 40 be less than 90%, morepreferably 80% or less, and most preferably 50% or less of the maximumintensity at the center of each beam. When the intensity of the beam issignificantly high so that exfoliation occurs at an intensity which ishalf (50%) the maximum intensity of the beam, overlapping at regions inwhich the intensity is higher than half of the maximum intensity may beavoided.

[0342] Such irradiation modes can also be applicable to beam shapes,such as a spot beam, other than a line beam. In the spot beam scanning,vertical and horizontal relationships between the adjacent irradiatedregions must be taken into account.

[0343] The direction of the incident light including laser light is notlimited to the direction perpendicular to the separation layer 120, andmay be shifted by a given angle from the perpendicular direction as longas the intensity of the incident light is substantially uniform in theseparation layer 120.

[0344] An example in accordance with the present invention will now bedescribed. The example corresponds to a modification of the laserirradiation in Example 1 of the third embodiment.

MODIFIED EXAMPLE 1

[0345] A quartz substrate with a length of 50 mm, a width of 50 mm, anda thickness of 1.1 mm (softening point: 1,630° C., distortion point:1,070° C., and transmittance of excimer laser: approximately 100%) wasprepared, and an amorphous silicon (a-Si) film as a separation layer(laser-absorption layer) was formed on the one side of the quartzsubstrate by a low pressure CVD process (Si₂H₆ gas, 425° C.). Thethickness of the separation layer was 100 nm.

[0346] A SiO₂ film as an interlayer was formed on the separation layerby an ECR-CVD process (SiH₄+O₂ gas, 100° C.). The thickness of theinterlayer was 200 nm.

[0347] A polycrystalline silicon (or polycrystalline silicon) film witha thickness of 50 nm as a transferred layer was formed on the interlayerby a CVD process (Si₂H₆ gas). The polycrystalline silicon film waspatterned to form source/drain/channel regions of a thin filmtransistor. After a SiO₂ gate insulating film was formed by thermaloxidation of the surface of the polycrystalline silicon film, a gateelectrode (a structure in which a high melting point metal, such as Mo,was deposited on the polycrystalline silicon) was formed on the gateinsulating film, and source and drain regions were formed by selfalignment by means of ion implantation using the gate electrode as amask. A thin film transistor was thereby formed.

[0348] A thin film transistor having similar characteristics can beformed by a low temperature process instead of such a high temperatureprocess. For example., an amorphous silicon film with a thickness of 50nm as a transferred layer was formed on a SiO₂ film as an interlayer onthe separation layer by a low pressure CVD process (Si₂H₆ gas, 425° C.),and the amorphous silicon film was irradiated with laser beams(wavelength: 308 nm) to modify the amorphous silicon into apolycrystalline silicon film by crystallization. The polycrystallinesilicon film was patterned to form source/drain/channel regions having agiven pattern of a thin film transistor. After a SiO₂ gate insulatingfilm was deposited on the polycrystalline silicon film by a low pressureCVD process, a gate electrode (a structure in which a high melting pointmetal, such as Mo, was deposited on the polycrystalline silicon) wasformed on the gate insulating film, and source and drain regions wereformed by self alignment by means of ion implantation using the gateelectrode as a mask. A thin film transistor was thereby formed.

[0349] Next, electrodes and leads connected to the source and drainregions and leads connected to the gate electrode were formed, ifnecessary. These electrodes and leads are generally composed ofaluminum, but not for the limitation. A metal (not melted by laserirradiation in the succeeding step) having a melting point higher thanthat of aluminum may be used if melting of aluminum is expected in thesucceeding laser irradiation step.

[0350] A UV-curable adhesive (thickness: 100 μm) was applied onto thethin film transistor, a large, transparent glass substrate (soda glass,softening point: 740° C., distortion point: 511° C.) as a transfermember was adhered to the adhesive film, and the outer surface of theglass substrate was irradiated with ultraviolet rays to fix these layersby curing the adhesive.

[0351] The surface of the quartz substrate was irradiated with Xe—Clexcimer laser beams (wavelength: 308 nm) to cause exfoliation (internaland interfacial exfoliation) of the separation layer. The energy densityof the Xe—Cl excimer laser was 250 mJ/cm², and the irradiation time was20 nano seconds. The excimer laser irradiation methods include aspot-beam irradiation method and a line-beam irradiation method. In thespot-beam irradiation method, a given unit area (for example 8 mm by 8mm) is irradiated with a spot beam, and the spot irradiation is repeatedwhile scanning the spot beam such that irradiated regions do not overlapwith each other (in the vertical and horizontal directions), as shown inFIG. 43. In the line-beam irradiation, a given unit area (for example378 mm □˜0.1 mm, or 378 mm □˜0.3 mm (absorbing 90% or more of theincident energy)) is irradiated while scanning the line-beam such thatirradiated regions do not overlap with each other, as shown in FIG. 43.Alternatively, irradiation may be performed such that the totalintensity of the beams is reduced in the doubly-irradiated region.

[0352] Next, the quartz substrate was detached from the glass substrate(transfer member) at the separation layer, so that the thin filmtransistor and interlayer formed on the quartz substrate weretransferred onto the glass substrate. The separation layer remaining onthe interlayer on the glass substrate was removed by etching, washing,or a combination thereof. A similar process was applied to the quartzsubstrate for recycling it.

[0353] When the glass substrate as the transfer member is larger thanthe quartz substrate, the transfer from the quartz substrate to theglass substrate in accordance with this example can be repeated to forma number of thin film transistors on different positions on the quartzsubstrate. A larger number of thin film transistors can be formed on theglass substrate by repeated deposition cycles.

[0354] [Eighth Embodiment]

[0355] An exfoliating method in accordance with the eighth embodiment ofthe present invention will now be described in detail with reference tothe attached drawings. In the eighth embodiment, the exfoliation memberor transferred layer in any one of the first to seventh embodiments iscomposed of a CMOS-TFT.

[0356] FIGS. 24 to 34 are cross-sectional views of the steps in theexfoliating method in this embodiment.

[0357] [Step 1] As shown in FIG. 24, a separation layer (for example, anamorphous silicon layer formed by a LPCVD process) 120, an interlayer(for example, SiO₂ film) 142, and an amorphous silicon layer (forexample, formed by a LPCVD process) 143 are deposited in that order on asubstrate (for example, a quartz substrate) 100, and then the entireamorphous silicon layer 143 is irradiated with laser light beams toanneal the layer. The amorphous, silicon layer 143 is thereby modifiedinto a polycrystalline silicon layer by recrystallization.

[0358] [Step 2] As shown in FIG. 25, the polycrystalline silicon layerformed by laser annealing is patterned to form islands 144 a and 144 b.

[0359] [Step 3] As shown in FIG. 26, gate insulating films 148 a and 148b are formed to cover the islands 144 a and 144 b, for example, by a CVDprocess.

[0360] [Step 4] As shown in FIG. 27, gate electrodes 150 a and 150 bcomposed of polycrystalline silicon or metal are formed.

[0361] [Step 5] As shown in FIG. 28, a mask layer 170 composed of apolyimide resin etc. is formed, and for example, boron (B) ision-implanted by self-alignment using the gate electrode 150 b and themask layer 170 as masks. p-Doped layers 172 a and 172 b are therebyformed.

[0362] [Step 6] As shown in FIG. 29, a mask layer 174 composed of apolyimide resin etc. is formed, and for example, phosphorus (P) ision-implanted by self-alignment using the gate electrode 150 a and themask layer 174 as masks. n-Doped layers 146 a and 146 b are therebyformed.

[0363] [Step 7] As shown in FIG. 30, an insulating interlayer 154 isformed, contact holes are selectively formed, and then electrodes 152 ato 152 d are formed.

[0364] The formed CMOS-TFT corresponds to the transferred layer (thinfilm device) shown in FIGS. 18 to 22. A protective film may be formed onthe insulating interlayer 154.

[0365] [Step 8] As shown in FIG. 31, an epoxy resin layer 160 as anadhesive layer is formed on the CMOS-TFT, and then the TFT is adhered tothe transfer member (for example, a soda-glass substrate) 180 with theepoxy resin layer 160. The epoxy resin is cured by heat to fix thetransfer member 180 and the TFT.

[0366] A photo-polymeric resin which is a UV-curable adhesive may alsobe used as the adhesive layer 160. In such a case, the transfer member180 is irradiated with ultra-violet rays to cure the polymer.

[0367] [Step 9] As shown in FIG. 32, the rear surface of the substrate100 is irradiated with, for example, Xe—Cl excimer laser beams in orderto cause internal and/or interfacial exfoliation of the separation layer120.

[0368] [Step 10] As shown in FIG. 33, the substrate 100 is detached.

[0369] [Step 11] The separation layer 120 is removed by etching. Asshown in FIG. 34, thereby, the CMOS-TFT is transferred onto the transfermember 180.

[0370] [Ninth Embodiment]

[0371] The use of transfer technologies of thin film devices describedin the first to eighth embodiments enables the formation of amicrocomputer composed of thin film devices on a given substrate, forexample, as shown in FIG. 35(a). In FIG. 35(a), on a flexible substrate182 composed of plastic etc., a CPU 300 provided with a circuitincluding thin film devices, a RAM 320, an input-output circuit 360, anda solar battery 340 having PIN-junction of amorphous silicon forsupplying electrical power to these circuits are mounted. Since themicrocomputer in FIG. 35(a) is formed on the flexible substrate, it isresistive to bending, as shown in FIG. 35(b), and to dropping because ofits light weight.

[0372] [Tenth Embodiment]

[0373] An active matrix liquid crystal display device, shown in FIGS. 36and 37, using an active matrix substrate can be produced by a transfertechnology of any one of the first to fourth embodiments.

[0374] As shown in FIG. 36, the active matrix liquid crystal displaydevice is provided with an illumination source 400 such as a back light,a polarizing plate 420, an active matrix substrate 440, a liquid crystal460, a counter substrate 480, and a polarizing plate 500.

[0375] When a flexible active matrix substrate 440 and a countersubstrate 480 such as plastic film are used, a flexible, lightweightactive matrix liquid crystal panel resistant to impact can be achievedby substituting a reflecting liquid crystal panel using a reflectiveplate instead of the illumination source 400. When the pixel electrodeis formed of metal, the reflecting plate and the polarizing plate 420are not required.

[0376] The active matrix substrate 440 used in this embodiment is adriver-built-in active matrix substrate in which a TFT is provided in apixel section 442 and a driver circuit (a scanning line driver and adata line driver) 444 is built in.

[0377] A circuit of a main section of the active matrix liquid crystaldisplay device is shown in FIG. 37. As shown in FIG. 37, in a pixelsection 442, a gate is connected to a gate line G1, and either a sourceor a drain is connected to a data line D1. Further, the pixel section442 includes a TFT (M1) and a liquid crystal 460, wherein the other ofthe source and drain is connected to the liquid crystal 460. A driversection 444 includes a TFT (M2) formed by the same process as for theTFT (Ml) in the pixel section 442.

[0378] The active matrix substrate 440 including TFTs (M1 and M2) can beformed by the transferring method in accordance with either the third orfourth embodiment.

INDUSTRIAL APPLICABILITY

[0379] In accordance with the present invention as described above,various types of exfoliation members (detached members) capable offorming on substrates are transferred onto transfer members which areother than the substrates which are used in the formation of theexfoliation members so that the exfoliation members are arranged on thetransfer members which are other than the substrates used in theformation of the exfoliation members. Accordingly, the present inventionis applicable to production of various devices including liquid crystaldevices and semiconductor integrated circuits.

What is claimed is:
 1. A transferring method, comprising: providing asubstrate; forming a transferred layer over the substrate; joining atransfer member to the transferred layer; and removing the transferredlayer from the substrate; transferring the transferred layer to thetransfer member; and reusing the substrate for another transfer.
 2. Thetransferring method according to claim 1, exfoliation being caused at atleast one of the separation layer and an interface between theseparation layer and the substrate, the transferred layer being removedfrom the substrate.
 3. The transferring method, according to claim 2,the separation layer being irradiated with light to cause theexfoliation.
 4. The transferring method according to claim 2, furthercomprising forming an adhesive layer over the transferred layer, theadhesive layer joining the transferred layer to the transfer member. 5.The transferring method according to claim 4, the adhesive layercomprising an adhesive selected from the group consisting of a curableadhesive, a reactive curing adhesive, a photo-setting adhesive, aheat-hardening adhesive, a UV-curing adhesive and an anaerobic adhesive.6. The transferring method according to claim 5, the substrate havingtransparency, and being illuminated from the substrate side to hardenthe adhesive.
 7. The transferring method according to claim 4, thetransfer member having transparency, and being illuminated from thetransfer member to harden the adhesive.
 8. The transferring methodaccording to claim 1, the transferred layer comprising at least one of athin film semiconductor device including a thin film transistor and athin film diode, an electrode, a photovoltaic device, an actuator,micro-magnetic device, an optical thin film, a superconducting thin filmand a multi-layered thin film.
 9. The method of manufacturing an activematrix substrate, comprising: forming a separation layer over thesubstrate; forming a transferred layer, including a plurality of thinfilm transistors, above the substrate; removing the transferred layerfrom the substrate; transferring the transferred layer to the transfermember; and reusing the substrate for another transfer.
 10. The methodfor manufacturing an active matrix substrate according to claim 9, theactive matrix substrate comprising a pixel portion and a driver portion,at least one of which having the transistor.
 11. A transferring method,comprising: providing a substrate; forming a separation layer over thesubstrate; forming a transferred layer over the separation layer; andpartly cleaving the separation layer such that a part of the transferredlayer is transferred to a transfer member in a given pattern.
 12. Thetransferring method, according to claim 11, an exfoliation being causedat at least one of the separation layer and an interface between theseparation layer and the substrate, the transferred layer being removedfrom the substrate.
 13. The transferring method, according to claim 12,the separation layer being partly irradiated with light to cause theexfoliation.
 14. The transferring method, according to claim 13, thelight being irradiated through a mask.
 15. The transferring method,according to claim 13, a position for the irradiation being controlled.16. The transferring method of claim 11, the separation layer beingrepeatedly transferred to the transfer member.
 17. The transferringmethod of claim 16, the transfer member being larger than the substrate.18. The transferring method of claim 16, the transferred layer beingtransferred side by side in the repeating cycle.
 19. The transferringmethod according to claim 11, further comprising forming an adhesivelayer over the transferred layer, the adhesive layer joining thetransferred layer to the transfer member.
 20. The transferring methodaccording to claim 19, the adhesive layer comprising an adhesiveselected from the group consisting of a curable adhesive, a reactivecuring adhesive, a photo-setting adhesive, a heat-hardening adhesive, aUV-curing adhesive and an anaerobic adhesive.
 21. The transferringmethod according to claim 20, the substrate having transparency, andbeing illuminated from the substrate side to harden the adhesive. 22.The transferring method according to claim 20, the transfer memberhaving transparency, and being illuminated from the transfer member toharden the adhesive.
 23. The transferring method according to claim 11,the transferred layer comprising at least one of a thin filmsemiconductor device including a thin film transistor and a thin filmdiode, an electrode, a photovoltaic device, an actuator, micro-magneticdevice, an optical thin film, a superconducting thin film and amulti-layered thin film.
 24. A method for manufacturing an active matrixsubstrate, comprising: providing a substrate; forming a separation layerover the substrate; forming a transferred layer including a plurality ofthin film transistors, above the separation layer; and partly cleavingthe separation layer such that a part of the transferred layer istransferred to a transfer member in a given pattern, repeatedly.
 25. Thetransferring method of claim 24, the transfer member being larger thanthe substrate.
 26. The method of manufacturing an active matrixsubstrate according to claim 24, the active matrix substrate comprisinga pixel portion and a driver portion, at least one of which has thetransistor.
 27. A transferring method, comprising: providing asubstrate; forming a transferred layer over the substrate; joining atransfer member to the transferred layer; removing the transferred layerfrom the substrate; transferring the transferred layer to the transfermember; and joining the transfer member, removing the transferred layerand transferring the transferred layer constituting a transfer process,the transfer process being repeatedly performed.
 28. The transferringmethod, according to claim 27, exfoliation being caused at at least oneof the separation layer and an interface between the separation layerand the substrate, the transferred layer being removed from thesubstrate.
 29. The transferring method, according to claim 27, theseparation layer being irradiated with light to cause the exfoliation.30. The transferring method, according to claim 27, the transfer processbeing repeatedly performed for an even number of times.
 31. Thetransferring method according to claim 27, further comprising forming anadhesive layer over the transferred layer, the adhesive layer joiningthe transferred layer to the transfer member.
 32. The transferringmethod according to claim 31, the adhesive layer comprising an adhesiveselected from the group consisting of a curable adhesive, a reactivecuring adhesive, a photo-setting adhesive, a heat-hardening adhesive, aUV-curing adhesive and an anaerobic adhesive.
 33. The transferringmethod according to claim 32, the substrate having transparency, andbeing illuminated form the substrate side to harden the adhesive. 34.The transferring method according to claim 31, the transfer memberhaving transparency, and being illuminated from the transfer member toharden the adhesive.
 35. The transferring method according to claim 27,the transferred layer comprising at least one of a thin filmsemiconductor device including a thin film transistor and a thin filmdiode, an electrode, a photovoltaic device, an actuator, micro-magneticdevice, an optical thin film, a superconducting thin film and amulti-layered thin film.
 36. A method for manufacturing an active matrixsubstrate, comprising: forming a separation layer over the substrate;forming a transferred layer, including a plurality of thin filmtransistors, above the substrate; joining a transfer member to thetransferred layer; removing the transferred layer from the substrate;transferring the transferred layer to the transfer member; and joiningthe transfer member, removing the transferred layer and transferring thetransferred layer constituting a transfer process, the transfer processbeing repeatedly performed.
 37. The method for manufacturing an activematrix substrate according to claim 36, the active matrix substratecomprising a pixel portion and a driver portion, at least one of whichhas the transistor.